What Is the Strait of Hormuz and Why Is It Important?

The U.S. strikes on Sunday brought the United States into that war, heightening fears among American allies and adversaries of a dangerously escalating conflict across the region. American military and intelligence officials detected potential signs that Iran-backed militias were preparing to attack American bases in Iraq, and possibly Syria.

Iranian officials appeared to be weighing their options for retaliation against the United States. Foreign Minister Abbas Araghchi was expected to meet with President Vladimir V. Putin of Russia on Monday. Even though Russia is a longtime Iranian ally, there has been little sign so far that it is prepared to provide military assistance to Iran in this war.

More than 24 hours after U.S. bombers hit three uranium-enrichment sites in Iran, prompting President Trump to declare that Iran’s nuclear program had been “totally obliterated,” the actual state of the program seemed far more murky, with senior officials conceding they did not know the fate of Iran’s stockpile of near-bomb-grade uranium. And world leaders and diplomats were scrambling to prevent more violence. E.U. foreign ministers discussed the situation in Iran on Monday. The war, and the U.S. strikes will likely dominate a NATO summit that opens at The Hague on Tuesday.

Trump administration officials emphasized on Sunday that the United States did not want an all-out war with Tehran, but Mr. Trump’s position was less clear — particularly when he raised the prospect of regime change in Iran in a social media post on Sunday. He was set to meet with his National Security Council on Monday.

Another question is how the widening war will affect the global economy. Asian markets dipped on Monday, reflecting investor concern over possible economic fallout from the U.S. strikes and any potential moves by Iran to disrupt shipping through the Strait of Hormuz, a critical transit point for global oil supplies.

Here’s what else to know:

• Potential damage: Mr. Trump has said Iran’s nuclear sites were “obliterated” in the attack, but Pentagon officials have struck a more cautious tone by describing the damage to three sites — at Fordo, Natanz and Isfahan — as “severe.” Senior officials have also conceded they did not know the whereabouts of Iran’s supply of near-bomb-grade uranium.

• Possible response: Mr. Trump’s decision to attack Iran seemed likely to dim hopes for a negotiated solution to end the fighting, only days after the president had indicated he would wait for as long as two weeks to give diplomacy a chance. While U.S. officials say that Iran has depleted its stockpile of medium-range missiles, the country still has an ample supply of other weapons, including rockets and drones.

• The strikes: Pentagon officials described a tightly choreographed operation that included B-2 bombers carrying 30,000-pound bunker-buster bombs and submarine-fired Tomahawk cruise missiles hitting a trio of sites in less than a half-hour. A senior U.S. official acknowledged that the attack on Fordo had not destroyed the heavily fortified site, but it had been severely damaged.

River Akira Davis contributed reporting.

In more than a week of fighting between Israel and Iran, Israel’s military has steered clear of hitting Iranian naval assets. So while Iran’s ability to respond to attacks has been severely damaged, it has a robust navy and maintains operatives across the region, where the United States has more than 40,000 troops. Iran also has an array of mines that its navy could lay in the Strait of Hormuz, which hugs a portion of Iran’s southern border.

A quarter of the world’s oil and 20 percent of the world’s liquefied natural gas passes through the Strait of Hormuz, so mining the choke point would cause oil and gas prices to soar. The majority of those fuels go to Asia, meaning that countries there would most likely be severely affected by any closure. The United States and other countries would feel the effects in the form of higher energy costs.

Closing the waterway could isolate American minesweepers in the Persian Gulf on one side of the strait. Two defense officials indicated that the Navy was looking to disperse its ships in the gulf so that they would be less vulnerable. A Navy official declined to comment, citing operational security. The officials spoke on condition of anonymity because they were not authorized to speak publicly.

Even before the U.S. military struck Iranian nuclear sites over the weekend, Iran vowed that it would respond forcefully to any attack by American forces — potentially setting off a cycle of escalation. Since the strikes, Iran appears to be weighing its options.

“Iran is strategically weaker but operationally still lethal across the region, and Americans still have troops across that part of the world,” said Brian Katulis, a senior fellow at the Middle East Institute.

Military officials and analysts said missile and drone attacks remained the biggest retaliatory threat to U.S. bases and facilities in the region. Some also worry that the Quds Force, a shadowy arm of Iran’s military, could attack U.S. troops.

Much is at stake for Iran if it decides to retaliate. “Many of Iran’s options are the strategic equivalent of a suicide bombing,” said Karim Sadjadpour, an Iran policy expert at the Carnegie Endowment for International Peace. “They can do enormous damage to others if they mine the Strait of Hormuz, destroy regional oil facilities and rain a missile barrage against Israel, but they may not survive the blowback.”

But Iran can make it hugely expensive, and dangerous, for the U.S. Navy to have to conduct what would most likely be a weekslong mine-clearing operation in the Strait of Hormuz, according to one former naval officer who was stationed on a minesweeper in the Persian Gulf. He and other Navy officers said that clearing the strait could also put American sailors directly in harm’s way.

Mining the strait would also inflict severe economic damage in Iran because nearly all of the country’s oil exports move through the channel.

President Trump has long criticized the Iraq war, called for the withdrawal of U.S. troops from Afghanistan and once pledged to end the “era of endless wars.”

But over the weekend, the United States struck three nuclear sites in Iran, in an effort to support Israel in its war against Iran, potentially kicking off a more dangerous phase in the conflict.

‘I’ll give him the benefit of the doubt.’

Bruce Bell, 39, Stockbridge, Mich.

Bruce Bell was at his home on Saturday night, scrolling on his phone when he saw the news of the strikes on Iran.

His reaction was wait and see.

“I agree with most people that war is bad,” he said. “But I don’t know enough about this situation with Iran. I keep hearing about red lines and how they’ve been encroaching for a while.”

Mr. Bell, a transmission mechanic, has drifted politically. He voted for former President Barack Obama twice, and then chose a third-party candidate for president in 2016.

In 2020, he decided to vote for Mr. Trump. He liked how Mr. Trump talked about the border and about manufacturing. And Mr. Bell did not like what felt to him like the Democratic Party’s progressive political stance on policing.

He voted for Mr. Trump again in 2024.

“I’ve seen a lot of blustering from politicians,” he said. “Then someone like Trump comes in and does something. He just sort of detonates the situation — and this is kind of his M.O. It’s like our Southern border — everyone says it can’t be secured, and then he comes in and does it.”

Foreign policy issues are not the top priority for Mr. Bell. When it comes to the bombing, he said, “I’ll give him the benefit of the doubt. I do want to see the follow-ups and see information on why and hope and pray that there were not any innocent casualties.”

— Sabrina Tavernise

‘One of the big reasons I voted for him was him keeping us out of stuff in the Middle East.’

Charles Vaughters, 24, Laramie, Wyo.

When Charles Vaughters, a college student and Marine veteran, heard the news of the bombings in Iran, he said that he couldn’t help but feel somewhat betrayed.

“One of the big reasons I voted for him was him keeping us out of stuff in the Middle East,” Mr. Vaughters said of Mr. Trump, adding that the countries in that region should be left to settle their disputes themselves.

He called the president’s move “a step too far” and said that he had spoken with other young Trump supporters in the red state of Wyoming who felt the same way.

“We’ve definitely had our trust shaken,” he said.

Mr. Vaughters, who is a history major at the University of Wyoming, supported Mr. Trump in the last two elections. Mr. Vaughters was drawn in, he said, by the president’s “America First” platform and by his promises to stay out of foreign wars and to bring back manufacturing to the country. So the administration’s bombing of another country seems “a little hypocritical,” Mr. Vaughters said, adding that he still supported the president and did not regret voting for him.

Now, though, Mr. Trump has put the United States in a precarious position, Mr. Vaughters said, by threatening further military action against Iran, while so many U.S. troops are based in the region. He fears that an Iranian strike on a U.S. base could trigger a push for ground troops, which he said would be “absolutely disastrous.”

As for what Mr. Trump should do next, Mr. Vaughters said, “If I were him, I’d just really, really keep trying to push negotiations between Iran and Israel.” He added that Mr. Trump should tell Israel: “OK, we’ve done the strike for you. Now, Israel, we are totally out of this. Figure it out on your own.”

— Juliet Macur

‘Every time you show weakness, they take advantage.’

Edward Padron, 67, Brownsville, Texas

Edward Padron was a young Army private when American hostages were taken in 1979 at the United States Embassy in Iran.

Mr. Padron, now a locksmith who lives in a border city, said that Mr. Trump was finally doing what former President Jimmy Carter had tried, but failed, to do — take military action in Iran.

“We would have shown the Middle East that you don’t mess with the United States,” he said. “I was there when it started. Donald Trump is doing what Jimmy Carter should have done.”

Tensions with Iran have continued since, and Mr. Padron is confident that the Trump administration chose to attack Iran because it was close to getting an atomic bomb, even though U.S. intelligence had assessed that Iran was not.

“They were the ones who poked the United States in the eye and said, What are you going to do about it?” Mr. Padron said.

Mr. Padron said he also supported the U.S. invasion of Iraq under former President George W. Bush because Saddam Hussein had become an enemy of the U.S., even if the so-called weapons of mass destruction never materialized.

“Every time you show weakness, they take advantage,” he said.

Mr. Padron thinks Mr. Trump had little choice but to bomb Iran’s nuclear sites. Now, he said, Iran must come to the table and negotiate and prevent a larger war. “It is in their hands,” he said.

— Edgar Sandoval

‘We voted for him because he would stay out.’

Noel Estrada, 32, Eagle, Colo.

In the mountains of Colorado, Noel Estrada was driving home from a camping trip without cell service on Sunday morning when his phone lit up with a belated flood of news about the bombing.

“It’s upsetting,” said Mr. Estrada, who fixes vending machines and A.T.M.s. “We voted for him because he would stay out.”

Mr. Estrada did not doubt that Iran could be pursuing a nuclear weapon, but he said the attack had nothing to do with his overriding concern in life: the high cost of living. Mr. Estrada said he had voted for Mr. Trump in the hopes that he could bring down gas and food prices, which are even higher in the mountain towns where Mr. Estrada lives and works.

To him, the bombing of Iran’s nuclear facilities felt like a diversion from the fact that groceries were still too expensive and he was still paying taxes on his overtime wages, as lawmakers in Washington fight over Mr. Trump’s budget bill. And the bombing, he said, represented a broken promise from a politician who ran on opposing America’s involvement in “stupid wars.”

“There’s no need for war,” Mr. Estrada said. “He said he was a friendly president and didn’t want wars. And here we are, six months in.”

— Jack Healy

The bombing ‘was protecting this little, tiny nation, but I don’t think that we need to be there further.’

Naomi Villalba, 75, Dallas

Naomi Villalba said she supported Mr. Trump’s decision to bomb nuclear sites in Iran. She feared that the country was developing a nuclear weapon specifically for Israel because of its democratic government and religion.

But she also said she believed that Iran was an exception to Mr. Trump’s campaign promise of not getting involved in foreign wars, and that she did not support more U.S. involvement.

Mr. Trump, she said, has been consistent: “We’re not the police of the world, we’re a protector. That’s it. And so I think that was protecting this little, tiny nation, but I don’t think that we need to be there further.”

Ms. Villalba is also worried that the military action on Iran may prompt additional unrest and protests.

“I think because we’re so divided in the United States, that so many have been fed — because they have not lived on the planet as long as I have — indoctrinations that are really just outlandish, and so I’m hoping that it doesn’t cause more unrest in our nation.”

— Christina Morales

‘I’m hoping that his campaign promises were true.’

Erwin McKone, 55, Flint, Mich.

Every day, Erwin McKone stands in the shower and thinks about how lucky he is to have hot water running through his pipes. Lately, he has also been thinking about how he does not have to worry about war and his house rattling with the sounds of bombs or explosions.

Mr. McKone supported Mr. Trump’s decision to strike three Iranian nuclear sites, and would support further military action, because he believes strongly that Islamic extremist groups should not have access to a nuclear weapon.

However, he is torn about the effects on innocent people in Iran, and about the potential invitation for retribution that could harm American civilians.

Mr. McKone said he struggled to vote for Mr. Trump in November because of how “reckless with his words” he could be. Despite the action on Iran, Mr. McKone believes the president is still committed to peace.

“I do think that he isn’t going to drag us into bigger wars,” said Mr. McKone, who voted for Mr. Trump in part because of his antiwar campaign promises. “I think the goal is de-escalation, and the goal is less death and destruction, but I guess that remains to be seen.”

“I’m hoping that his campaign promises were true,” he added.

— Sonia A. Rao

In the battle for global narratives, China has long cast the United States as a warmonger and a destabilizing power while presenting itself as a responsible global leader championing peace and fairness.

At an emergency meeting of the Security Council on Sunday, Mr. Fu said that China condemned the U.S. strikes and was joining Russia and Pakistan in drafting a U.N. resolution calling for a cease-fire, the safety of civilians and a start to peace negotiations.

The criticism of the United States was echoed in Chinese state media reports on Monday, with the official news agency, Xinhua, accusing the United States of escalating violence in the region.

“The worsening situation in the Middle East is a stark reminder that power politics and military interventions lead to nothing but chaos and instability,” the article said.

In a separate editorial on Monday, the Communist Party tabloid, the Global Times, said the U.S. strikes had weakened “the foundation of the international security order.”

On China’s heavily censored internet forums, users have left furious comments about how Iran was deceived into thinking it was negotiating a nuclear agreement with the United States, only to lower its guard and become the target of U.S. bombs.

China’s rhetoric belies a more complicated reality. Beijing has been one of Tehran’s biggest backers, diplomatically and economically. Its purchases of almost all of Iran’s oil exports have helped a brutal Iranian regime stay in power and deliver support to its terrorist proxies abroad, including Hamas, Hezbollah and the Houthis.

It remains to be seen how China might use its influence over Iran as fears of a broader conflict grow. Secretary of State Marco Rubio on Sunday urged China to persuade Tehran not to make good on a threat to close the Strait of Hormuz, one of the world’s most vital waterways for the transport of oil.

“China will certainly oppose Iran” closing the strait, said Wang Yiwei, the director of the Institute of International Affairs at Renmin University in Beijing, because of China’s need for access to Iranian oil. But it would only do so on its terms and in its own time, he suggested.

“However, it would be improper, or even counterproductive, to discuss this with the United States, or to exert pressure on Iran at the request of the United States,” he added.

When asked on Monday what China would do if Iran closed the strait, Guo Jiakun, a spokesman for the Foreign Ministry, deflected and called on the international community to “step up its efforts to promote the de-escalation of the conflict.”

Sirens are now wailing in central Israel in response to additional missile fire, according to the Israeli military.

Israeli fighter jets attacked surface-to-surface missile launchers and storage sites in Kermanshah, the military later said, calling it part of Israel’s broader aim of degrading Iran’s military capabilities.

The price of West Texas Intermediate, the benchmark for U.S. crude oil, was up roughly 1 percent, paring some of their increases. Gold, a traditional safe-haven asset, also rose. Futures contracts for the S&P 500, indicating how the index might perform when markets open in New York, were up slightly.

Traders were waiting for clearer indications of whether there would be an escalation in conflicts in the Middle East — particularly any moves by Iran that might disrupt oil shipments through the Strait of Hormuz.

The Strait of Hormuz is a critical transit point for global oil supplies. Last year, about 20 million barrels of oil were shipped through the waterway each day, representing about 20 percent of the world’s total supply. Most of that oil was bound for Asia.

Places like Japan and Taiwan rely on the Middle East for almost all of their crude oil imports, meaning that any disruption to traffic through the passageway could inflict a large economic blow. China is the largest purchaser of Iranian oil.

Oil prices, hovering around $76 a barrel, are expected to reach $80, but if the risk of Iran blocking the Strait of Hormuz increases, so will the price of oil, said Takahide Kiuchi, executive economist at Nomura Research Institute. In that case, “the Japanese economy could be exposed to downside risks that exceed those of the Trump tariffs,” he said.

Other analysts expect fallout from the U.S. strikes to be relatively short-lived.

The oil market is better equipped to respond to shocks than it has been in the past because of spare capacity held by exporters, according to Daniel Hynes, a senior commodity strategist at ANZ Research. Geopolitical events involving producers can have a big impact on oil markets, but in recent years, prices have tended to quickly retreat as risks ease, Mr. Hynes said.

Daniel Ives, an analyst at Wedbush Securities, said there could be more volatility in stock movements this week. But, he said, the market may view the Iran threat as “now gone.” In that case, he said, “the worst is now in the rearview mirror.”

Joe Rennison contributed reporting from New York.

One day after the administration announced it had carried out airstrikes at three nuclear sites in Iran, the mood in some communities around military bases on U.S. soil varied from firm support to bitter disagreement. But one sentiment stood out among those interviewed: concern for the safety of America’s troops everywhere.

No one knows how the strikes on Iran could affect service members. Pete Hegseth, the secretary of defense, emphasized on Sunday that the administration did not want an open-ended war. But Iranian leaders have vowed to retaliate, and U.S. military installations in the Middle East, with more than 40,000 active-duty troops and civilians employed by the Pentagon, are already potential targets.

That reality, along with the potential repercussions for the entire military, was on the minds of many people around U.S. bases at home, even as service members accepted that reality as part of the job.

“A lot of the families around here are quickly realizing this is a real threat; this is something we need to be worried about,” said Meghan Gilles, 37, a self-described military brat who works in the Army Reserve’s human resources division at Fort Campbell in Kentucky, a training site and home to the 101st Airborne Division.

At Eglin Air Force Base in Florida, Blake Carlson, a 23-year-old Army National Guard combat medic who was visiting from Austin, Texas, said that he could be deployed. “It’s what I signed up for,” he said. “If I have to, I’ll do it.” But his mother and brother hoped the country would not be dragged into the escalating conflict in the Middle East.

Some people who were interviewed stood by Mr. Trump and agreed with his assertions that the targeted bombings were unlikely to lead to a wider conflict. Mr. Carlson’s mother, Tonya Carlson, said she hoped the attack would force Iran to negotiate with the United States.

Others stood by Mr. Trump’s statement that Iran posed an imminent threat — a point that contradicts recent national security assessments. “Iran doesn’t need to have nuclear weapons, for sure,” said Tony Saluzzo, 72, a former combat engineer who served in the U.S. offensive against Iraq and lives near Fort Campbell.

James Arthur, a 42-year-old retired Coast Guard captain who lives north of Tampa, Fla., and was visiting the Air Force Armament Museum at the Eglin base, said that the Iran airstrikes happened “about two decades too late.”

Other former service members castigated Mr. Trump for bombing Iran without congressional approval. The Constitution’s framers included language to ensure that wars would not be entered rashly, said Paul Oyler, a Navy veteran who served in Iraq and Afghanistan and who lives near the Naval Air Station Lemoore in California, where he was based while on active duty.

He said he would have agreed with the airstrikes if there were a proven, credible threat to the region, but “I don’t have any reason to believe that Iran was in possession of actual nuclear weapons.”

Denver Thiery, 30, who works on military maintenance contracts and lives in Trenton, Ky., near Fort Campbell, said he would remain firmly behind Mr. Trump. But he also acknowledged that it was difficult to know exactly what capabilities Iran possessed.

“I don’t know the truth of what’s going on,” he said. “I don’t know if they really have nuclear warheads or not. I don’t know what I can support anymore.”

Ms. Gilles, the reservist, whose father is a veteran and whose husband is an active-duty serviceman, was troubled by the decision to edge the country to war at the very moment the government was cutting funding for Veterans Affairs.

The administration is taking away a lot of benefits for veterans and “then just sending them off again to be the world police,” Ms. Gilles said.

If the current conflict worsens, military members and veterans said, they would put aside their disagreements over Mr. Trump and support one another. But one veteran lamented what he said such a scenario would ultimately mean.

“I learned from my time on active duty that war is devastating,” Mr. Oyler said.

John Ismay contributed reporting.

The Iranians have made it clear they are not interested in having conversations with the United States, accusing Washington of deceiving Tehran during the last set of negotiations while planning the air attack. Moreover, that stockpile of fuel is now one of the few nuclear bargaining chips in Iranian hands.

In a briefing for reporters on Sunday, Defense Secretary Pete Hegseth and the new chairman of the Joint Chiefs of Staff, Dan Caine, avoided Mr. Trump’s maximalist claims of success. They said an initial battle-damage assessment of all three sites struck by Air Force B-2 bombers and Navy Tomahawk missiles showed “severe damage and destruction.”

Satellite photographs of the primary target, the Fordo uranium enrichment plant that Iran built under a mountain, showed several holes where a dozen 30,000-pound Massive Ordnance Penetrators — one of the largest conventional bombs in the U.S. arsenal — punched deep holes in the rock. The Israeli military’s initial analysis concluded that the site, the target of American and Israeli military planners for more than 26 years, sustained serious damage from the strike but had not been completely destroyed.

But there was also evidence, according to two Israeli officials with knowledge of the intelligence, that Iran had moved equipment and uranium from the site in recent days. And there was growing evidence that the Iranians, attuned to Mr. Trump’s repeated threats to take military action, had removed 400 kilograms, or roughly 880 pounds, of uranium enriched to 60 percent purity. That is just below the 90 percent that is usually used in nuclear weapons.

The 60-percent enriched fuel had been stored deep inside another nuclear complex, near the ancient capital of Isfahan. Rafael Mariano Grossi, the director general of the International Atomic Energy Agency, said by text that the fuel had last been seen by his teams of United Nations inspectors about a week before Israel began its attacks on Iran. In an interview on CNN on Sunday he added that “Iran has made no secret that they have protected this material.”

Asked by text later in the day whether he meant that the fuel stockpile — which is stored in special casks small enough to fit in the trunks of about 10 cars — had been moved, he replied, “I do.” That appeared to be the mystery about the fuel’s fate that Mr. Vance was discussing.

If so, Isfahan would not be the only place where the custodians of the Iranian nuclear program — a subject of nationalistic pride and the symbol of Iran’s ability to defend itself — were trying to move equipment and material out of sight, and harden the Fordo plant to protect what had to stay in place.

Satellite images released by Maxar Technologies at the tunnels leading into the Fordo mountain, taken in the days before the American strike, show 16 cargo trucks positioned near an entrance. An analysis by the Open Source Centre in London suggested that Iran may have been preparing the site for a strike.

It is unclear exactly what, if anything, was removed from the facility.

In fact, there was only so much the Iranians could save. The giant centrifuges that spin at supersonic speeds, purifying uranium, are piped together and bolted to the cement floor. One U.S. official said it would have been unrealistic to completely move equipment out of Fordo after the conflict with Israel began.

The official added that historical documents about the nuclear program were buried in the bowels of the site, likely complicating any efforts in reconstituting it. In coming days, both the Iranians and intelligence agencies expect to learn more about the Natanz enrichment site, which is older, larger and less well protected than Fordo. It was struck by the Israelis repeatedly, and they destroyed an aboveground enrichment center and disrupted the electrical system. Mr. Grossi later said he believed the interruption of the electrical supply could have sent the centrifuges spinning out of control, probably destroying all of them.

How long it would take the Iranians to repair and replace that equipment is unknown; it would probably stretch for years. But Iran is also building a new, deep replacement for Natanz in the south of the city. Officials in Tehran have told the I.A.E. A. that they have not yet opened the plant, so there is nothing to see.

If Iran is truly pursuing a nuclear weapon — which it officially denies — it is taking more time than any nuclear-armed nation in history. The United States developed the Manhattan Project in four years or so, developing the bombs dropped at Hiroshima and Nagasaki to end the war in the Pacific. The Soviet Union conducted its first test in 1949, only four years later. India, Pakistan and Israel all sped the process.

The Iranians have been at it for more than 20 years, and an archive of data stolen from a Tehran warehouse by Israel a number of years ago showed that Iranian engineers were exploring nuclear triggers and other equipment that would only be used to detonate a weapon. That was around 2003, when, according to American intelligence, the engineers received instructions to halt work on weaponization.

Comments by Mr. Trump and Prime Minister Benjamin Netanyahu in recent days suggest they believe that work has resumed, though no evidence to support the contention has been made public. If so, the strikes on Fordo, Natanz and Isfahan may only reinforce the view among Iranian leaders that they need a weapon for survival of the government.

History also suggests that diplomacy has usually been more effective than sabotage or military attacks in providing assurances that a country does not pursue atomic weapons. More than 15 years ago, the joint U.S.- Israeli attack on Natanz, using a sophisticated cyber weapon, caused about a fifth of the country’s 5,000 or so centrifuges to blow up.

But the Iranians not only rebuilt, they installed more sophisticated equipment. Before Israel’s attack this month, they had roughly 19,000 centrifuges in operation.

It was only when the Obama administration struck the 2015 nuclear deal with Iran that the United States got a fuller picture of its capabilities, thanks to the work of inspectors. And those inspections were choked off — and many security cameras disabled — after Mr. Trump declared the nuclear accord a “disaster” and withdrew from it.

Tehran’s reaction was to scale up centrifuge production, enrich uranium at levels only weapons states need, and stonewall the I.A.E.A.

Now, it is unclear whether the team of I.A.E.A. inspectors who were in the country when the conflict with Israel broke out will be permitted by the Iranian government to resume their inspections, which would include verifying the whereabouts and the safety of that near-bomb-grade uranium.

All international inspections have been suspended during wartime, Iranian officials have said. And even if they were to resume, it was unclear the inspectors could physically gain access to the bombed Fordo underground plant, or the wreckage of the larger enrichment facility at Natanz.

Mick Mulroy, a former Pentagon official in the first Trump administration and a former C.I.A. officer, said of the strike: “With the type and amount of munitions used, it will likely set back the Iranian nuclear weapon program two to five years.”

Vice President JD Vance argued that Mr. Trump had “clear authority to act to prevent the proliferation of weapons of mass destruction.”

However, later on Sunday, Mr. Trump wrote online that his military aims could be much more expansive: “If the current Iranian Regime is unable to MAKE IRAN GREAT AGAIN, why wouldn’t there be a Regime change??? MIGA!!!”

Criticisms of the attack, which came less than two weeks after Israel began its bombing campaign against Iran, include Mr. Trump not giving American policymakers, lawmakers and the public enough time to debate a role in a conflict that experts warn could grow quickly if Iran retaliates.

The furor over the sudden strikes follows years of bipartisan efforts in Congress to try to place greater limits on a president’s ability to order military action, efforts that arose because of disastrous American wars in the Middle East and Central Asia.

So is the United States at war with Iran? And did Mr. Trump have the authority to order his attack without consulting Congress?

What does the U.S. Constitution say about war?

Article I, Section 8 of the Constitution assigns Congress dozens of powers like collecting taxes and creating post offices, as well as the power to “declare war” and to “raise and support armies.”

The Constitution’s framers considered that clause a crucial check on presidential power, according to an essay by the law professors Michael D. Ramsey and Stephen I. Vladeck for the National Constitution Center. Early in American history, Congress approved even limited conflicts, including frontier clashes with Native American tribes.

But the question is complicated by Article II of the Constitution, which delineates the powers of the president, and which designates the U.S. leader as the “commander in chief” of the U.S. military.

Presidents of both parties, relying heavily on legal opinions written by executive-branch lawyers, have cited that language to justify military action without congressional involvement.

Congress tried asserting itself with the War Powers Resolution of 1973, which says the American president must “consult with Congress before introducing United States Armed Forces into hostilities or into situation where imminent involvement in hostilities is clearly indicated by the circumstances.”

But presidents have repeatedly disregarded that language or argued for a narrow definition of the “introduction” of forces. Congress has done little to enforce the resolution.

What are members of Congress saying about the U.S. strikes?

Democrats have almost uniformly criticized Mr. Trump for acting without legislative consent, and a few Republicans have as well.

“His actions are a clear violation of our Constitution — ignoring the requirement that only the Congress has the authority to declare war,” Senator Chris Van Hollen, Democrat of Maryland, said in a statement echoed by many of his colleagues.

Representative Thomas Massie, Republican of Kentucky, told CBS News that there was no “imminent threat to the United States” from Iran.

Senator Tim Kaine, Democrat of Virginia, said on the same CBS program that Congress must act this week to assert a role in any further U.S. military action.

“Would we think it was war if Iran bombed a U.S. nuclear facility? Of course we would,” Mr. Kaine said. “This is the U.S. jumping into a war of choice at Donald Trump’s urging, without any compelling national security interests for the United States to act in this way, particularly without a debate and vote in Congress.”

Some Democrats say Mr. Trump has already gone unforgivably far. Representative Alexandria Ocasio-Cortez of New York called on Saturday night for Mr. Trump’s impeachment.

Hawkish Republicans rejected such talk. “He had all the authority he needs under the Constitution,” Senator Lindsey Graham of South Carolina told NBC News on Sunday. Mr. Graham cited Mr. Trump’s power as commander in chief under Article II of the Constitution.

“Congress can declare war, or cut off funding. We can’t be the commander in chief. You can’t have 535 commander-in-chiefs,” Mr. Graham said, referring to the combined number of U.S. representatives and senators. “If you don’t like what the president does in terms of war, you can cut off the funding.”

Mr. Graham noted that Congress has made formal war declarations in only five conflicts, and none since World War II. However, there has been a legal equivalent from Congress that President George W. Bush was the last American leader to successfully seek: an authorization for the use of military force, often called an A.U.M.F.

What are legal scholars saying?

Several lawyers and scholars who have studied the international law of armed conflict say the United States is without a doubt at war with Iran for purposes of application of that law, and that Mr. Trump acted in violation of international conventions.

“The short answer is that this is, in my view, illegal under both international law and U.S. domestic law,” said Oona Hathaway, a professor of international law at Yale Law School who has worked at the Defense Department.

Brian Finucane, a former lawyer at the State Department, agreed that Mr. Trump needed to ask Congress for authorization beforehand. He also said “there is certainly a U.S. armed conflict with Iran, so the law of war applies.”

On Sunday, Iran’s foreign minister, Abbas Araghchi, called the U.S. attack an “outrageous, grave and unprecedented violation” of international law and of the United Nations charter, which forbids U.N. members from violating the sovereignty of other members.

Mr. Araghchi did not specifically say that his country is now at war with America. Mr. Finucane also said the United States had violated the U.N. charter.

Ryan Goodman, a law professor at New York University who has also worked at the Defense Department, said “one important matter for both domestic law and especially international law is the issue of ‘imminence.’”

The Trump administration is justifying the U.S. attack by saying Iran’s development of a nuclear weapon was imminent, Mr. Goodman noted.

But “the law would require that the attack would be imminent,” he said, and “it is very hard to see how the administration can meet that test under even the most charitable legal assessment.”

Even if one were to focus on the question of a nuclear bomb, U.S. intelligence agencies have assessed that Iran had not yet decided to make such a weapon, even though it had developed a large stockpile of the enriched uranium necessary for doing so.

How often have presidents sought congressional approval for war?

In the decades since Congress declared war on Japan and Germany in 1941, U.S. presidents have repeatedly joined or started major conflicts without congressional consent.

President Harry S. Truman sent U.S. forces into Korea. President Ronald Reagan ordered military action in Libya, Grenada and Lebanon; President George H.W. Bush invaded Panama; President Bill Clinton ordered the bombing of mostly Serbian targets in Yugoslavia during the Kosovo War; President Barack Obama joined a 2011 NATO bombing campaign against the government of Muammar Qaddafi in Libya and led a military campaign against the Islamic State in Syria and Iraq.

Mr. Obama broke with this trend in September 2013 when he decided against launching a planned strike against Syria without first seeking congressional authorization. The strike was unpopular in Congress, which never held a vote, and Mr. Obama did not act.

President George W. Bush won separate congressional authorizations for the use of military force against Afghanistan and Iraq before ordering invasions of those countries in 2001 and 2003.

In the years since the Al Qaeda attacks of Sept. 11, 2001, several presidents have also ordered countless airstrikes and special operations raids on foreign soil to kill accused terrorists. Those have largely relied on broad interpretations of the two authorizations for the use of military force that Congress granted the executive branch for the so-called war on terror.

Emma Ashford, a scholar of U.S. foreign policy at the Stimson Center, said that in the post-9/11 wars, “some presidents have largely stopped asking permission at all.”

In January 2020, Mr. Trump chose not to consult Congress before ordering an airstrike that killed a senior Iranian military commander, Qassim Suleimani, while he was visiting Iraq. Many members of Congress called that a clear act of war that was likely to begin wider hostilities. Iran responded by firing 27 missiles at U.S. forces in Iraq, inflicting traumatic brain injuries on about 100 U.S. troops. But the conflict did not expand further.

Last year, President Joseph R. Biden Jr. ordered U.S. airstrikes against the Houthi militia in Yemen without getting congressional permission, and Mr. Trump did the same this year.

Advances in military technology, including drones and precision-guided munitions, have allowed presidents to take action with minimal initial risk to U.S. forces. Military officials say that Saturday’s strike in Iran, carried out by B-2 stealth bombers, encountered no resistance.

But critics say the action invites Iranian retaliation that could escalate into full-scale war.

What happens next

G.O.P. leaders in the House and Senate have signaled support for the strike, but Democrats and a few Republicans are demanding that Congress approve any further military action.

Mr. Kaine, who serves on the committees on armed services and foreign relations, introduced a Senate resolution last week requiring that Mr. Trump get explicit congressional approval before taking military action against Iran. Mr. Kaine on Sunday said the measure was still relevant and that he hoped it would come to a vote this week.

Mr. Massie, the Kentucky Republican, introduced a similar war powers resolution last week in the House with Ro Khanna, Democrat of California.

“When two countries are bombing each other daily in a hot war, and a third country joins the bombing, that’s an act of war,” Mr. Massie wrote on social media on Sunday.

Mr. Massie said he was “amazed at the mental gymnastics” Mr. Trump’s defenders have employed to argue the United States was not entering a war by attacking Iranian nuclear facilities.

Megan Mineiro contributed reporting.