Since World War II, presidents of both parties have found ways to hollow out the Constitution’s constraints on their power to order military attacks. President Trump’s unilateral decision to launch a war against Iran threatens to gut nearly all of what little remains.
It is supposed to be a foundational principle of American democracy that unless the United States is under attack, the power to declare war is vested in Congress. But especially since the start of the Cold War, presidents of both parties have chipped away at that by claiming a right to order the military into various limited hostile situations.
Some lawmakers complained. But as an institution, Congress acquiesced. Consistently paralyzed by competing impulses — party loyalty, support for the policy goals of various deployments or fear of being accused of undercutting troops already in harm’s way — lawmakers let presidents get away with serial power grabs.
Successive administrations built on their predecessors’ innovations, a one-way ratchet expanding the circumstances in which presidents had claimed and demonstrated that they could by themselves deploy troops into combat. As precedents accumulated, the split between how the founders clearly intended decisions about initiating war to be made and how the country was governed in practice kept widening.
Even so, the prospect of attacking Iran, absent a literally imminent threat of attack by the country, had stood apart as a textbook example of what would seemingly still require congressional authorization. The potential for rapid spiraling — of retaliatory strikes on U.S. citizens, troops and allies in neighboring countries, of escalation into a bloody regional conflagration with global economic consequences — seemed too extreme a risk for any one person to decide to take on.
Asked to detail its legal analysis, the White House provided a brief statement that described decades of misdeeds by Iran, claiming that Mr. Trump “exercised his authority as commander in chief to defend U.S. personnel and bases in the region.”
It is not clear whether the administration’s internal legal analysis relies on any claim that Iran posed an imminent threat. Neither the White House statement nor a letter Mr. Trump sent to Congress said it did.
But in public statements, Mr. Trump and Secretary of State Marco Rubio, who also serves as the national security adviser, have invoked that phrase. Mr. Trump went on to say it would be intolerable to allow Iran time to develop a nuclear weapon and long-range missiles — apparently relying on a very elongated view of what counts as imminent.
Mr. Rubio said that Israel was going to attack Iran and that it was likely that Tehran’s response would include firing missiles at American bases, so the United States joined the attack “proactively, in a defensive way.” In addition to its circularity, this argument is premised on the idea that Mr. Trump could not have instead restrained Israel.
Process is no guarantee. Some presidentially ordered operations have gone smoothly, while the congressionally authorized wars in Afghanistan and Iraq are widely considered fiascoes. But given such risks, the question is who the founders thought should decide, and whether that still means anything.
The House is set to take up a resolution directing Mr. Trump to cease the war without congressional authorization, but the Senate defeated the same measure Wednesday in a nearly party-line vote. Even if it passed both chambers, the president could veto it.
Regardless, Mr. Trump has already established a new precedent. His Iran war expands the scope of the kinds of “major combat operations” that presidents in the modern era have demonstrated they can start on their own authority. Executive branch lawyers will be able to cite this moment as support for blessing future unilateral presidential war-making.
A remnant of a line remains uncrossed for now: While Mr. Trump briefly sent ground forces into Venezuela in January, accepting the risk of U.S. casualties, he has yet to put boots on the ground in Iran. It appears his plan is to avoid doing so.
Still, in a letter notifying lawmakers two days after he started the war, Mr. Trump warned that while he “desires a quick and enduring peace, it is not possible at this time to know the full scope and duration of military operations that may be necessary.”
Jack Goldsmith, a Harvard Law professor and former senior Justice Department official in the George W. Bush administration, said Mr. Trump’s unilateral launch of the Iran war may be remembered as the death of any pretense that law and executive branch lawyers can be counted on to meaningfully constrain a president who wants to use military force on his own.
“By using the military on such a large and dangerous scale with foreseeable U.S. casualties, this operation kills the idea of any effective legal constraint on the president’s use of force,” he said. “It’s been very close to dead for years, I think.”
Iran and Escalation
In 2007, Senator Joseph R. Biden Jr. argued in a presidential candidate survey that presidents have no legitimate power to bomb another country without congressional authorization, unless the United States is about to be attacked. Senator Barack Obama said the same thing. But executive power can look different from the vantage point of the Oval Office.
Mr. Obama bombed Libya without authorization in 2011. And, running for president again in 2019, Mr. Biden argued that the Constitution empowered presidents to order limited military strikes on their own. In 2024, Mr. Biden ordered several large-scale strikes on Iranian-backed Houthi militants in Yemen who were menacing Israel and shipping in the Red Sea.
Against that backdrop, Mr. Biden’s approach to Iran over time is instructive. In 2007, he had singled out an attack on the country as particularly dangerous and unpredictable, writing, “Let’s not kid ourselves: any military conflict with Iran is likely to become major.”
In 2019, he maintained that “any initiation of the use of force against Iran,” unless in response to an imminent attack, “could certainly result in a wide-scale conflict and constitute a ‘war’ in the constitutional sense that would require authorization by Congress.”
But as president in 2023, before he dropped out of the 2024 race, Mr. Biden sidestepped Iran in responding to a similarly worded survey.
Mr. Trump had already joined Israel last June in bombing Iranian nuclear sites, in what has become known as the 12-day war. Since then, he has unilaterally “determined” that the United States is in a formal armed conflict with drug cartels, and launched a brief invasion of Venezuela to seize its president, Nicolás Maduro.
Now, without going to Congress, Mr. Trump has joined Israel in killing Iran’s supreme leader and other top officials at the start of a massively larger bombing campaign that he said he intended to last “four to five weeks.” He has urged Iranians to rise up for a regime change.
Ahead of the operation, Mr. Trump made scant effort to persuade lawmakers and the public that such a war had become necessary. He delivered no Oval Office address and barely mentioned Iran in his State of the Union speech, a sharp divergence from how past presidents sought to build a case for wars they wanted to launch.
Those past campaigns have drawn accusations of spin and deception, as when the George W. Bush administration’s warnings about Iraqi weapons of mass destruction proved false after the war began. But even propaganda is a backhanded nod to democracy — an implicit acknowledgment that buy-in from Congress and the public matters when it comes to taking the country to war.
Eroding Constraint
While Mr. Trump’s open indifference to law and norms of self-restraint has pushed presidential war-making powers to a new extreme, he is also extending a path that the country was already on. For generations, presidents in the modern era have steadily eroded constraints on their power to initiate military actions.
The 18th century British king had the power to decide to take his country to war and the power to direct it. Having rebelled against rule by that monarchy, the United States’ founders sought to separate those powers as “a great principle in free government,” as James Madison wrote in 1793.
“Those who are to conduct a war cannot in the nature of things, be proper or safe judges, whether a war ought to be commenced,” Madison wrote, adding that the aggrandized power and honors the executive enjoys in wartime means “the temptation would be too great for any one man.”
This system did not always work perfectly, but a practical constraint helped enforce the broad legal principle: The United States did not maintain large standing armies in peacetime. But rather than demobilizing after World War II, the United States kept forces deployed around the world. Presidents of both parties began ordering them into new hostilities on their own.
In 1950, President Harry S. Truman took the country into the Korean War without going to Congress. He pointed to authorization by the new United Nations Security Council, but that did not matter for the domestic law question of who had the rightful power to decide whether the United States would participate.
No president had ever launched such a war effort without seeking congressional permission, but Congress did not impeach him.
In 1973, after bipartisan recognition that the Vietnam War had been a disaster, lawmakers sought to regain their constitutional role in deciding whether to go to war. They enacted, over President Richard M. Nixon’s veto, the War Powers Resolution.
The act established mechanisms by which Congress could, in theory, end unauthorized deployments. And it laid out a limited vision of when presidents could deploy troops into hostile situations on their own — essentially, only if the country was under attack.
For the three largest wars since then — the Persian Gulf War and the wars in Afghanistan and Iraq — presidents went to Congress for authorization. They also serially stretched the Afghanistan war law, which targeted Al Qaeda, by interpreting it as approval to battle other militant groups with Qaeda links in countries like Syria and Somalia. Congress acquiesced.
The new Iran war appears likely to be the most aggressive and significant military operation undertaken since 1973 without any claim of congressional approval.
Chipping Away
Republican and Democratic administrations have interpreted the War Powers Resolution narrowly. Since it was enacted, every president has deployed troops into limited hostile situations that went beyond the act’s narrow parameters, like trying to rescue Americans in places like Cambodia and Iran; peacekeeping missions in places like Lebanon, Somalia and Bosnia; and NATO air wars in Kosovo and Libya.
Blessing such operations as lawful, the Justice Department’s Office of Legal Counsel has argued that the president has constitutional power to deploy troops into hostile situations in the national interest, so long as the anticipated intensity, scope and duration fall short of “war” in the constitutional sense.
Executive branch lawyers have produced a series of memos blessing unilateral deployments by pointing to various factors that they said meant what the president wanted to do met that standard. But the pattern over time has been that when subsequent proposed deployments lack such factors, the Office of Legal Counsel has found ways to approve them, too.
In a recent essay analyzing a memo approving Mr. Trump’s invasion of Venezuela, Rebecca Ingber, a professor at the Cardozo School of Law and a former senior State Department lawyer, showed how it “cherry-picked the powers” suggested by a 2011 memo approving airstrikes in Libya and a 2018 memo approving airstrikes in Syria, but “ignored the constraints” in them.
“The decades of O.L.C. memoranda authorizing force in new ways, each assembling the factors from prior tests without ever laying out specific limits, provide fertile ground for such cherry- picking,” she observed.
“There is one thing,” he said. “My own morality. My own mind. It’s the only thing that can stop me, and that’s very good.”
But Professor Goldsmith said that while law has been revealed as toothless as an internal executive branch check on unilateral presidential war-making, there was still politics.
“Courts can’t do anything, there is clearly zero internal check and that literally means that all that is left is Congress and the people,” he said. “That might amount to nothing, but it’s literally all that is conceivably left.”
