Congress Gave Away Its Authority To Declare War and Enabled Trump’s Iran War

President Donald Trump and his administration have long claimed that he wants to chart a more restrained path for America’s foreign policy. Before the 2024 presidential election, running mate J.D. Vance dubbed Trump the “candidate of peace.” Trump broke with Republican Party orthodoxy during a 2016 presidential debate when he called the war in Iraq “a big, fat mistake.” Yet a decade later, his administration is embroiled in a conflict that looks a lot like the one he decried.

The U.S. and Israel launched strikes against several targets in Iran on February 28, killing Ayatollah Ali Khamenei, the country’s supreme leader. Since then, Iran has struck several U.S. diplomatic offices and military facilities in the Middle East, while the U.S. has hit missile and oil sites across Iran. As of mid-April, 13 American service members had died in the war, which showed few signs of slowing down. The U.S. reportedly was weighing larger deployments to the region, and at press time Trump had not ruled out putting American boots on the ground.

The Trump administration offered a wide range of justifications for its military actions in Iran, which Congress did not authorize. As Reason‘s Matthew Petti wrote in March, officials said they sought “to preempt a possible Iranian attack (which other officials say wasn’t real), to join in an Israeli attack that was going to happen ‘with or without the United States,’ to take advantage of a fleeting opportunity to kill Iranian leadership, or to punish Iran for failing to give in to U.S. demands [for nuclear concessions] in time.”

The Constitution grants Congress the sole power to declare war. But constitutional control of warmaking has fallen so far to the wayside that presidents no longer feel obliged to present a coherent case for military action to Congress. Congress, meanwhile, has helped render itself toothless on matters of war.

Congress last voted to declare war in 1942, when it authorized action against Bulgaria, Hungary, and Romania during World War II. Since then, U.S. military action has been approved via congressional authorizations for the use of military force (AUMFs) or unilateral presidential decisions.

AUMFs are joint resolutions that give the president broad discretion to involve U.S. military assets in conflicts. Without sunset provisions, they remain on the books for decades and can be invoked to justify military skirmishes far beyond their intended purposes. The 2001 AUMF, which authorized the president “to use all necessary and appropriate force” against any “nations, organizations, or persons” involved in the September 11 attacks, had been cited to justify counterterrorism activities in 22 countries as of 2020, Brown University’s Costs of War project reported.

Presidents have additional tools at their disposal to use and misuse. The 1973 War Powers Resolution “opens the door for presidents to engage in smaller-scale or short operations,” Rochester Institute of Technology political scientist Sarah Burns notes. But presidents have tried to flout some of the law’s requirements.

President Barack Obama “claimed the War Powers Resolution did not apply” to “his bombing campaign in Libya in 2011,” Burns writes. “President George H.W. Bush deployed hundreds of thousands of U.S. troops to the Persian Gulf region before Congress had taken a vote to authorize it,” NPR’s Ron Elving noted in 2020. Other examples of congressionally unauthorized military action include President Bill Clinton’s interventions in Bosnia and Kosovo, Obama’s battles with ISIS in Iraq and Syria, Trump’s first-term interventions in the Middle East, and his second-term operation in Venezuela.

Since passing the War Powers Resolution more than 50 years ago, Congress typically has not even attempted to reclaim its war authority. And on the rare occasions when Congress does try, the president can resist. Trump vetoed a 2019 congressional resolution calling for an end to U.S. involvement in Yemen’s civil war, and a 2020 resolution challenging his unilateral action in Iran met the same fate.

“Both parties have been feckless in allowing the growth of the power of the presidency,” Sen. Cory Booker (D–N.J.) observed during a March appearance on CNN. “At this scale, at this magnitude, at this cost, why is Congress just laying down and doing nothing?”

In February, Sens. Tim Kaine (D–Va.) and Rand Paul (R–Ky.) filed a resolution challenging the Trump administration’s war in Iran. It failed by a nearly party-line 47–53 vote in early March. Reps. Ro Khanna (D–Calif.) and Thomas Massie (R–Ky.) spearheaded a similar effort in the House, which would have been nonbinding and “merely would have stated Congress’s view that the president could not initiate major combat operations against Iran on his own authority,” as Council on Foreign Relations senior fellow James M. Lindsay notes. That faltered too.

Under constitutional constraints, a president has to justify military action to Congress. He must convince democratically elected representatives to publicly back that action in ways their constituents can track and challenge. Trump’s actions in Iran circumvent those important checks. They remind us that it is far easier to prevent an unjustified war from starting than it is to stop one in its tracks.