The Supreme Court ruled 6-3 last Friday that President Donald Trump exceeded his authority in imposing sweeping emergency tariffs – and some observers took it as a hopeful sign that institutions like the Court can still check presidential power even in foreign policy. In a sense, they are right. The Supreme Court struck down the tool at the heart of Trump’s foreign policy.
But the ruling on tariffs comes against the backdrop of the massive U.S. military buildup in the Middle East for a potential attack on Iran. And there, any optimism about the tariff ruling runs into a hard political reality: The constraints on presidential power that matter most are not the ones making headlines.
Analysts like Daniel Drezner and Caitlin Talmadge have argued that a U.S. strike against Iran would be a war of choice. Trump has said almost nothing about his goals or why the urgency to strike Iran now. In fact, Trump claimed last year – contrary to U.S. intelligence estimates – that the strikes he ordered in June “obliterated” Iran’s nuclear program.
Can anyone constrain Trump if he decides to attack Iran?
It’s very unlikely.
Congress won’t stop Trump from attacking Iran
Let’s start with Congress. When commentators talk about a potential attack on Iran (or Venezuela, or Syria, or many other military targets in the last couple of decades), they rightly note that any such attack by the United States would legally require congressional authorization. Calling for Congress to authorize an attack on Iran may be legally correct, but we’re long past the time when any U.S. president would treat the lack of congressional authorization as a real constraint.
Since 9/11, Congress has delegated more and more power on national security matters to the president. As a result, the de facto power to make war rests in the president’s hands. Harvard Law School professor Jack Goldsmith stated this bluntly after the Trump-authorized strike that killed Iranian General Qasim Soleimani in January 2020:
…our country has – through presidential aggrandizement accompanied by congressional authorization, delegation, and acquiescence – given one person, the president, a sprawling military and enormous discretion to use it in ways that can easily lead to a massive war. That is our system: One person decides.
Goldsmith reiterated this point after the January 2026 operation to seize Venezuelan President Nicolas Maduro. Good Authority contributor Andrew Rudalevige has also made a similar point repeatedly, including about the June 2025 Iran strikes.
Nothing has changed to make that assessment less true. Presidents have precedents to rely on, the Justice Department can likely produce opinions supporting whatever the president wants to do, and the courts are highly unlikely to interfere in matters of war and peace. Congress has plenty of tools to slow the march to war, including funding conditions, oversight, and open debate that alerts the public to the risks. But over the last few decades, congressional willingness to wield these tools has declined to the point where presidents no longer fear their effects in the national security domain.
Don’t expect public opinion to constrain Trump, either
Public opinion is also unlikely to slow Trump down, should he want to attack Iran.
The Venezuela operation offers a sobering reminder of how quickly the political landscape shifts once a president acts. Before the invasion, an Economist/YouGov poll found that only 44% of Republicans supported using U.S. military force to overthrow Maduro. After the invasion, that number rose to 78%.
Another striking finding: Before the operation, 58% of Republicans said Trump should seek congressional authorization before using force in Venezuela. Within days of the invasion, that figure collapsed to 21%.
As Michael Tesler has shown many times here at Good Authority, public opinion on foreign policy, including war, tends to follow where politicians go. If a specific conflict drags on and costs mount, then public opinion can turn against the president. But as the U.S. engagement in Iraq showed, it usually takes a while. Even Democratic members of Congress were slow to make the Iraq War the focus of their 2006 midterm campaign. At least in terms of stopping an attack before it starts, there is little reason to believe public opinion will stop Trump.
Constraints often come from within an administration – but not this one
Some of the weakness of congressional and public constraint undoubtedly stems from intense partisan polarization. But checks from the legislature or the public are often slow and unwieldy. So what can constrain a president from going to war?
The historical record points to constraints from inside presidential administrations. Although the president chooses his team, advisers and cabinet officials may have their own views on particular decisions about the use of force and may well disagree with each other or with the commander-in-chief. As I argue in my book The Insiders’ Game: How Elites Make War and Peace, insiders can impose costs on presidents who disregard their advice. Those with their own stature, connections to members of Congress, or well-known views can cause political damage if they speak out against the president’s plans. Though they serve a particular president, insiders may have their own motives for going public, related to policy, politics, or their future careers. Even if they don’t speak publicly, they can pass information on to other officials or members of Congress, who can jam up the president’s agenda. A president who is sensitive to such costs might try to head them off by shifting course or making concessions to those insiders.
Consider the political capital George W. Bush spent in the lead-up to the 2003 Iraq War, as he sought authorization from both Congress and the United Nations. Going to the U.N. for authorization was a concession to Secretary of State Colin Powell, a skeptic of attacking Iraq and whose public backing of the war Bush very much wanted. The political drag from Congress and the U.N. didn’t prevent the war, but it planted the seeds of constraint that shaped later administration decisions about strategy.
An even more instructive parallel for the current moment may be Trump’s threats against North Korea in 2018. The Trump administration was reportedly considering a “bloody nose” strike – a limited military action intended to bring Pyongyang to the negotiating table, similar to the limited strike Trump is now weighing for Iran. What stopped it? Not Congress. Not the courts. Not public opinion.
Instead, it was internal resistance, led by Secretary of Defense James Mattis and others at the Pentagon. Trump’s pick for ambassador to South Korea, Victor Cha, publicly opposed the bloody nose approach as dangerously escalatory. The administration pulled Cha’s nomination, but also shelved the plan for a limited strike on North Korea. In the first Trump administration, internal constraints still worked.
The question in the second Trump administration is, who is the voice of caution that Trump would actually heed?
It is hard to identify that person in the current cabinet. Defense Secretary Pete Hegseth has shown no inclination toward institutional pushback. Likewise, there is little evidence that Secretary of State and National Security Advisor Marco Rubio would serve as a brake on military adventurism in the Middle East. Trump has deliberately populated his second administration with loyalists, seeking to avoid the independent-minded, experienced officials who slowed things down the first time around.
Meanwhile, the military posture is alarming. The Trump administration has now assembled a huge military presence in the Middle East. Trump says he will decide within 10 to 15 days whether to strike.
The tariff ruling matters, for trade policy and for defining the limits of the president’s emergency powers – in peacetime. But it would be a mistake to let the tariffs case generate false comfort about the prospects for war or peace with Iran. Trump faces virtually no constraints on his ability to use military force. He can decide to go to war the way a personalist ruler can.
The only question is whether Trump will choose to pull the trigger.
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