Erin Scott / Reuters

This story was updated on January 9, 2020 at 8:30am.

Following the U.S. drone strike that killed Qassem Soleimani last week, and the Iranian strikes on an Iraqi base housing U.S. troops earlier this week, the conflict between the United States and Iran appears to be teetering on a knife’s edge. The president did not request or receive authorization from Congress before taking the strike, and many are now calling on Congress to step up and do something to prevent the country from sliding into full-blown war. With the immediate crisis possibly defused—for the moment—now is the time for Congress to engage, and it has a number of tools at its disposal to do so.

As a formal matter, the U.S. Constitution gives Congress, not the president, the power to declare war. Most legal experts agree that the president holds some Article II power to act in self-defense against a truly imminent attack. But the U.S. government has yet to put forward any evidence—beyond platitudes—suggesting that this was the case. Barring that, executive-branch lawyers have long claimed authority for the president to use force when the risk of escalation is minimal, a justification that is not a reasonable option here. With some exceptions, a consensus appears to be emerging among war-powers scholars that the Soleimani strike was illegal.

So what is the upshot of this? The question is unlikely to end up before a court, and no judge can truly prevent the president from using force without congressional authority. Given that, is Congress’s power moot? What, if anything, can Congress actually do to reassert its institutional role? If—hypothetically speaking—a majority in Congress wanted to keep the president from taking us to war, could it?

Congress has a number of tools it can—and should—wield to check the president in the war-powers arena. Unfortunately, many of these require regular attention and care, and rather than cultivating its war-powers tools, Congress has been ceding ground to the president in this space for years. Thus, only some of what follows are tools that Congress can use now to seek to rein in the current conflict, whereas others are tools Congress should cultivate to prevent the country from ending up in this dire situation again.

First, Congress should debate the policy implications of war with Iran whether or not the president requests authorization. The Constitution gives Congress, not the president, the power to declare war not because the Framers flipped a coin, but because such a weighty question affecting the nation should only be made following a full public debate, during which public support either develops or does not. This requires holding hearings, calling for evidence from executive-branch officials, and scrutinizing the evidence as well as the government’s plans for the end game. The time to do so is now, and the House is presently poised to consider legislation seeking to constrain the president’s use of unilateral force against Iran.

In addition to the power to declare war, the Constitution gives Congress authority over how and whether to fund it. Defunding the U.S. military in the midst of a full-blown war will not be popular, which is why Congress should enact spending restrictions now prohibiting the president from using force against Iran without authority from Congress. Restrictions on the use of the armed forces are often included when Congress passes its annual appropriations bills funding the military. Congress just missed an opportunity to do so when it stripped similar provisions, which had overwhelmingly passed in the House, from the National Defense Authorization Act it recently passed.

Additionally, while this subject is on the mind of the public and squarely before members of Congress, they should reform the War Powers Resolution too. The War Powers Resolution is a 1973 law passed by Congress that set conditions on the president when he acts unilaterally, including reporting requirements and time limits. The WPR does not itself authorize the use of force—a common misconception—and in fact explicitly states that it does not, but it does recognize that there may be certain cases in which presidents need to act unilaterally. By doing so, some interpret this as Congress implicitly ceding some ground to the president.

Congress ought to reform the War Powers Resolution to more clearly define the narrow, exceptional circumstances in which Congress accepts that the president may constitutionally use unilateral force, namely only when the United States is under an actual armed attack it must repel, or one is so truly imminent that there is no time for consultation with Congress. Congress should also require that the president demonstrate in reporting to Congress concrete evidence for this claim, such that—even if some of the evidence must remain classified—Congress is able to vouch for its existence to the American people. And Congress should tighten reporting requirements on the president, including through better defining the trigger for when the requirement kicks in.

Even when it does authorize force, Congress should set outer parameters on that power, including sunset provisions requiring that presidents come before Congress to make the case that the continued use of force is necessary. In addition to asserting constitutional power to act unilaterally, presidents have through three administrations justified the continued use of force in an ever-expanding conflict under two statutory authorizations from Congress: the 2001 and 2002 Authorizations for Use of Military Force.

The 2001 AUMF authorized the president to use force against al-Qaeda and the Taliban following the 9/11 attacks. But the executive branch has, over two decades, stretched its interpretation of its authority under that statute to cover groups it deems to have “joined” that particular conflict, including the Islamic State, which did not exist in 2001. The 2002 AUMF authorized the president “to defend the national security of the United States against the continuing threat posed by Iraq.” Neither of these statutes can fairly be read to authorize force against Iran. But they both remain on the books, despite several administrations’ reliance on them for conflicts that bear no resemblance to their initial purpose, in part due to Congress’s collective-action problem in withdrawing them.

For these reasons, future AUMFs should always include sunset provisions. These provisions would force Congress to reengage every several years to debate the wisdom of continuing the conflict—or of expanding it to include new groups—rather than leaving it open indefinitely. This is all the more crucial considering what we now know to be presidents’ expansive interpretations of these statutes.

Finally, and perhaps most important given the reticence of many members of Congress to engage directly on substance, Congress has significant opportunities to shape the foreign policy of the United States indirectly, by managing the inner workings of the executive branch. The president may at times act unilaterally, but he does not act alone. Numerous executive-branch decision makers engage on matters of national security—such as gathering intelligence; drawing up options; considering the legality of action; presenting options to senior decision makers, including the president; and carrying out orders. As I have explored in greater detail in my scholarship, Congress has tools to structure that decision-making process, require specific consultations among its members, and weigh in on who those members should be.

In the case of Soleimani, some reports are now emerging as to how this process went down inside the executive branch. But one thing is sure: The president did not create the plan to target Soleimani himself. This matter was considered, debated, and discarded for years, which suggests that at least some officials inside the U.S. government, and not just the president, were advocates of targeting Soleimani. And someone—however ill-advisedly—put the option before him now.

Congress’s tools to structure executive-branch decision making cannot put that decision back in the box. But it can demand hearings on the process that was used and the state of the national-security decision-making process generally, interrogate officials on their reasons for providing the Soleimani-strike option to the president, and bolster protections for whistle-blowers as well as for members of the chain of command seeking to defy clearly unlawful orders (such as the president’s proposal to strike Iranian cultural sites). And Congress can require that the president provide legal justification based on concrete evidence, from both the Department of Justice and the State Department, to address the domestic- and international-law ramifications of the strike. Doing so would empower lawyers from both agencies in decision-making exercises going forward.

As the country stands on the brink of war, it may seem like a sideshow to think about law. A 230-year-old document may seem beside the point when the policy implications are so significant, and are being made by someone sitting in the Oval Office whom many do not trust to put the nation’s best interests first. But this is the point. The U.S. Constitution determines who gets to decide when to bring the nation to war. And it gives that decision not to the individual operating inside a black box, but to the branch of government that will debate this decision in front of all.

This is not and should not be a partisan matter. It is about Congress’s institutional prerogative, and its responsibility to the public as a whole. Congress may not hold the reins to the U.S. military, but it can provide the public with a full airing of the implications to the president’s actions. In demonstrating the importance of its role to the American people, Congress can ultimately protect its own legal authority—and maybe, just maybe, stop a war before it is too late.

This story is part of the project “The Battle for the Constitution,” in partnership with the National Constitution Center.

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