A week after launching the largest U.S. military operation in two decades, President Donald Trump has yet to explain why he decided to go to war with Iran. Instead, he seems to be testing a variety of rationales, sometimes changing the argument within days in the hope one will stick with the American people. Americans, especially American soldiers and taxpayers, should have been convinced of the reasons for war before the conflict began—not simply offered a handful of justifications after the fact. Trump’s choice to start a war first and then try to explain it later could lead to adverse outcomes for American national interests. Some of his war aims are commendable. But I’m bracing for the worst. To date, the costs of this war outweigh the benefits.

Shifting War Aims

When initially explaining (in a video posted on Truth Social, rather than an address from the Oval Office, as is the custom) his reasoning for the full-scale attack on Iran, President Trump cheered for revolution. Trump explicitly hoped that the American and Israeli joint operation to decapitate the Iranian theocracy—including the assassination of Supreme Leader Ali Khamenei and several other top Iranians officials—would create the permissive conditions for regime change. He called on the Iranian people to seize power. “When we are finished, take over your government. It will be yours to take. This will probably be your only chance for generations,” he said.

Iran’s supreme leader was a tyrant who murdered tens of thousands of his own people and supported terrorists who killed many Israelis and Americans. Helping the people of Iran to live in freedom is therefore a laudable goal. It would not only benefit the people of Iran; it would also advance the security interests of the United States. A democratic Iran would not support terrorists, kill its citizens, or pursue nuclear weapons. The end of dictatorship rarely leads smoothly to the emergence of democracy, as I discussed in a Substack piece last week. But sometimes repressive regimes do collapse.

Very quickly, however, the administration rolled back on pursuing this ambitious goal. Secretary of War Pete Hegseth (the renaming of the Department of Defense now seems to be more than just a symbolic move), stated unequivocally that the war was “not about regime change.” White House press secretary Caroline Leavitt omitted regime change when listing the administration’s war aims. And then, when asked if Iran’s Crown Prince Reza Pahlavi, the son of the last shah of Iran, might play a role in a transitional government in Iran, Trump threw him under the bus—just like he did to Venezuelan opposition leader Maria Corina Machado—speculating that an internal leader would be more appropriate. By the end of the week, Trump was offering no support to the tens of thousands of peaceful protestors slaughtered by the theocrats earlier this year. He even hinted that he was ready to talk to the autocrats still in power in Iran, telling Atlantic reporter Michael Scherer: “They want to talk, and I have agreed to talk, so I will be talking to them.”

But talk about what? Although still not clearly defined, Trump and others have hinted that they may want to negotiate a nuclear deal with Iran’s current leadership. Ending Iran’s nuclear program forever is most certainly a war aim that was proposed last week. Trump and his aides keep saying that “Iran cannot have a nuclear weapon,” but this has been a goal of every American president—Democratic or Republican—since the mullahs seized power in Iran four decades ago. There is nothing new here. The debate has always been about how to achieve that goal and then maintain it.

President Barack Obama deployed coercive economic power—supported by the entire UN Security Council, including China and Russia—to compel the ruling mullahs in Tehran to sign a deal constraining their nuclear weapons aspirations. The Joint Comprehensive Plan of Action (JCPOA), signed by the five UN Security Council members and Germany, blocked Iran’s capabilities to produce nuclear-grade uranium and plutonium in return for sanctions relief. It worked. While the JCPOA was in effect, there was no credible evidence to support the claim that Iran was developing a nuclear weapon.

In 2018, however, Trump withdrew from the JCPOA. He boasted that he could get a better deal. Not surprisingly, soon thereafter, Iran gradually began to enrich uranium at higher levels, reducing the “breakout time” needed to make a nuclear bomb. So, instead of more diplomacy, Trump and Israel decided in June 2025 to bomb Iran’s nuclear facilities to prevent Iran from obtaining a nuclear weapon. At the end of that 12-day war, Trump’s White House released a statement titled: “Iran’s Nuclear Facilities Have Been Obliterated – and Suggestions Otherwise are Fake News.”

Fast forward several months, however, and Trump and his team are saying that bombing these facilities again is the only way to prevent Iran from obtaining a nuclear weapon. So, either the bombing last summer did not achieve its objectives (and Trump deceived us back then), or the Iranian regime was amazingly capable of reconstituting its nuclear program. In either scenario, preventing Iran from obtaining nuclear weapons through periodic bombing would seem to require an open-ended military campaign. How often will we have to bomb in the future? Hopefully not every nine months. But every year? And how will we know if the mission has been accomplished? Has the last week of bombing destroyed their enriched uranium stockpile? How will we know? And how can we trust the Trump administration to tell us the truth about what our bombing has achieved, given that they did not report their limited successes accurately from last June?

But maybe, as Trump hinted last week, the president was only using coercive military power to compel the theocrats to sign a new nuclear deal. In other words, this war aims to get a deal that Obama secured without launching a full-scale war. Of course, Trump and team will claim that their deal—if they get one—will be superior to Obama’s deal. The JCPOA most certainly had its flaws. But Trump’s new Iran nuclear deal better be an incredible treaty, given the loss of life and treasure that has already been expended to try to achieve it.

An additional goal of Trump’s war floated last week was to eliminate Iran’s ballistic missile arsenal—in other words, conventional disarmament. Today, Iran’s missiles do not threaten the American homeland. That threat is at least a decade away. But Iranian missiles can threaten Israel, and after the US and Israeli attacks on Iran last June, Tehran unsurprisingly increased its missile production. We attacked, so they invested more in their military capabilities. We should expect a similar pattern after each war with Iran ends.

Weakening Iran’s conventional military capabilities advances the security interests of the United States and Israel. The fewer missiles, launchers, ships, and drones that autocratic Iran has, the better. But what percentage of these weapons must we destroy to achieve victory? 70%? 80%? 90%? How will we know if this objective has been achieved? And once the war is over, what will prevent the surviving regime in Iran from restarting production of these weapons? And why has the Trump administration determined that deterrence no longer works? It seemed to be working well before this war: the combination of assured destruction if attacked and robust missile defenses. Again, as with the apparent Trump strategy for preventing Iran from obtaining a nuclear weapon, will we now have to be at permanent war with Iran, striking every year or two just to give their arsenal another haircut? That sounds like the definition of a forever war to me.

Stopping Tehran from funding terrorist organizations is another goal that was articulated last week to justify this war. Again, reducing support for Hamas, Hezbollah, the Houthis, and other jihadists is a worthy goal. But after October 7, 2023, didn’t Israel succeed in dramatically reducing the capabilities of these terrorist groups? Why was a new war needed now? Moreover, if we wanted to squeeze Iran’s finances, couldn’t we have imposed more comprehensive sanctions on its energy exports without going to war? The regime reported that they earned $65.8 billion in the Iranian calendar year ending in March 2025. OPEC’s estimate for 2024 was $46.8 billion. These numbers suggest that more and better sanctions could have been imposed on the Iranians government to reduce revenues transferred to terrorists without bombing.  And like with the other alleged objectives of this war, how will we know when this mission of the war has been accomplished? Bombing does not permanently disrupt bank transfers.

Another reason for war floated by the Trump administration last week was the claim that Iran has been at war with us since 1979, so we finally had to respond. As evidence for this, Trump officials referenced, among other incidents, the taking of American hostages in 1979 and the killing of American marines in 1983 by Tehran-backed terrorists. It is a tragic fact that the leaders of the Islamic Republic of Iran have killed, kidnapped, and terrorized Americans. But why did Trump decide to avenge these crimes now? Why didn’t he talk about the 1983 terrorist attacks during his first term? Or during his reelection campaign? Why didn’t he explain to the American people the need to finally respond to the “death to America” chants, popularized by the Iranian regime, before going to war? Tragic events from decades ago do not represent “imminent threats” to the United States today. War must always be a last resort to achieve American aims after all other instruments have been exhausted.

Last week, Secretary of State Marco Rubio floated an additional reason for the war: Israel made us do it. He explained that Israel was planning an attack on Iran that would have triggered an Iranian military response against American armed forces in the region. So instead of waiting, Trump allegedly decided to join Israel in launching a preemptive attack to reduce the blow of Iran’s response. Of course, another policy option would have been to convince Israel not to attack! American presidents, Republicans and Democrats alike, have been doing that for decades. But Rubio’s creative rationale for war triggered such blowback that Trump contradicted his Secretary of State and claimed that it was Israel who was following the United States.

Are you still tracking all the various arguments for war? Good. Because it’s about to get even more complicated. After starting the week by walking back the most ambitious goal of regime change, Trump seemed to reverse course by the week’s end, saying that the goal of the war must be “unconditional surrender.” Trump also argued that he would have to be involved in choosing Iran’s next leader and said that Iran’s borders will not look the same after the war is over. So, are we back to regime change as the goal? Territorial disintegration? I’m confused.

The Costs of War

If Trump could experiment with these changing goals at no cost, it would matter less which one he was truly pursuing. But obviously, that is not the case. This is a major war. This is a costly war.

Tragically, seven American soldiers have already died. Trump has warned that more will likely die before his war ends; he’s probably right. The Trump administration has even hinted that it might authorize a special forces operation to try to seize Iran’s stockpile of highly enriched uranium buried near the ancient city of Isfahan. Sending U.S. soldiers – even the best in the world – to undertake such a risky assignment would risk more American casualties.

Innocent civilians in Iran and the region have also been killed, including, most tragically, 175 school children and their teachers and staff in the bombing of a school. Accurately reporting on the number of total dead and wounded in this war is hard, but the number ranges in the thousands already. That number will continue to go up.

In addition, Trump’s war is expensive. Conservative estimates put the cost at roughly $1 billion a day—a significant amount that is not being spent on outcomes that American voters wanted. Discontent with inflation was a major reason Trump was reelected in 2024, yet this war has already driven up gas prices, and most economists expect further increases. As a presidential candidate in 2024, Trump did not pledge to wage war against Iran. Just the opposite. He promised to avoid the “forever wars” of his predecessors. In a doubling down on the Monroe Doctrine, his National Security Strategy made the case for why the United States should focus its attention on the Western Hemisphere. Iran is not in the Western Hemisphere.

More generally, Trump’s war in Iraq is pulling U.S. military attention back to the Middle East after Presidents Obama, Trump in his first term, and Biden have tried to pivot our military towards Asia. The successful use of the American military in Iran might serve as a deterrent for Chinese leaders. Our soldiers did not make the decision to go to war, but given the order, they are executing the plan very successfully. This display of American military might should frighten future potential foes. At the same time, U.S. armed forces will emerge from this war, whenever it ends, with depleted stockpiles that could take years to get back to full strength. Our ability to deter a potential PRC invasion of Taiwan is substantially less today than it was a week ago. We can build it back, but that will take time. It will also be costly.

In addition, Trump’s war has also exacerbated polarization in American society, at a time when American society is already deeply polarized. Votes in Congress last week showed a split down party lines; Republicans support Trump’s war, and Democrats do not (compare this with the Iraq war, when 77 of 100 senators voted in favor of intervention). Usually, Americans rally around the flag during times of war. A solid majority of Americans backed Bush in 2003. Trump, however, began his war with most Americans against it. That’s new. And this percentage is likely to increase over time if patterns of support for previous American wars are any guide.

Trump’s war of choice against Iran is also straining relations with allies and partners. When President Bush launched his war against Iraq in 2003, he did so with the support of four dozen countries. Trump launched his war with just one partner—Israel. European allies are trying desperately to avoid getting directly involved in the war, but without offending Trump. Asian allies, especially South Korea, are very worried about disruptions to oil supplies. Global oil prices are skyrocketing, and reserves in many countries are dwindling, making Trump’s war very unpopular among countries dependent on Middle East oil and gas. Tragically, Putin’s Russia is the one country benefiting most directly from skyrocketing fossil fuel prices.

Another cost of this war is to America’s reputation around the world. Trump and his supporters do not seem to care at all about how people in Africa, Asia, or Latin America perceive us. But for those countries that have previously experienced colonialism or intervention by great powers, this American war of choice looks imperial and unconstrained by international law, norms, or rules. American cheerleaders for Trump’s war seem to have forgotten the reputational damage our country endured after the Iraq War. Trump did not even try to present his case for war with Iran to the UN Security Council, unlike Obama did before using force in Libya in 2011, George W. Bush before invading Iraq in 2003 (though he failed to secure approval), or George H.W. Bush before going to war in Iraq in 1991. Americans may think the UN no longer matters. Billions around the world disagree with us.

How It Ends

It is a reflection of our current political environment that Trump has been able to take the United States into a war that few Americans wanted, that he never mentioned on the campaign trail, and that received neither congressional authorization, nor UN or NATO approval. Voters will only have the opportunity to hold Trump accountable after the fact. It should have been the other way around. But it was not, because Trump did not know how to explain this war to the American people. A week into the conflict, and he is still having trouble doing so.

This war will not end when regime change is accomplished, Iran’s nuclear program is permanently dismantled, a certain percentage of Iranian conventional weapons are destroyed, or financial support for terrorism is depleted. This war will end when Trump decides to end it, regardless of actual progress towards these multiple objectives. He will end the war when he feels like it, just like he explained he started it, based on gut instinct. Then he will, of course, declare victory.

And then the American people—first in the mid-term elections in November 2026 and then in a presidential election in November 2028—will have to decide if the costs were worth the benefits. That will be a hard calculation to make if the war’s actual goals have not been articulated by then.

Michael McFaul is a professor at Stamford, advisor to the Ukrainian government and the former US ambassador to Russia.

This comment first appeared in his substack here. Subscribe to his substack here.