Editor’s Note: Jonathan Cristol is a research fellow in the Levermore Global Scholars Program at Adelphi University and senior fellow at the Center for Civic Engagement at Bard College. Follow him on Twitter @jonathancristol. The views expressed in this commentary are his own. View more opinion on CNN.

(CNN) —  

On Tuesday, President Donald Trump vetoed a bipartisan congressional resolution that would have forced his administration to end military support for Saudi Arabia in the war in Yemen. This resolution was the first time that Congress has invoked the 1973 War Powers Resolution (often referred to as the “War Powers Act”), which limits the President’s ability to commit US forces abroad without congressional approval.

In addition to the significance of the veto itself, Trump’s decision could lead to a Supreme Court ruling on the constitutionality of the War Powers Resolution, which would dramatically expand or limit the President’s power to use military force abroad.

Jonathan Cristol
PHOTO: Simone Salvo
Jonathan Cristol

The War Powers Resolution was passed in 1973 – in response to what was seen as the unilateral commitment of the executive branch to long-term military engagements in Korea and Vietnam. The basic provisions of the resolution are easy to understand. The President must inform Congress within 48 hours any time “that United States Armed Forces are engaged in hostilities outside the territory of the United States.” He has a free hand to act for 60 days, but if Congress does not authorize his actions in that window of time, then he has an additional 30 days to safely withdraw the troops.

For over 40 years, Congress has not invoked its authority under the War Powers Resolution. Why? Because presidents have sought congressional authorization for their actions and informed Congress within 48 hours. In fact, presidents have done so more than 165 times since the resolution was passed.

But there’s another reason Congress has not invoked the resolution: concern that it might not be constitutional.

Article 2, Section 2 of the United States Constitution states that, “The President shall be Commander in Chief of the Army and Navy of the United States.” Congress is given the power to declare war, control military funding and “make Rules for the Government and Regulation of the land and naval Forces.” Nowhere does it have the authority to deploy forces abroad or to order their withdrawal.

Thus, the War Powers Resolution could arguably be an unconstitutional limitation on executive power. But we don’t know, because there has never been cause for a court decision – until now.

This resolution came in the wake of the murder of Washington Post columnist Jamal Khashoggi on the order of Saudi crown prince Mohammed bin Salman (MBS denies any involvement). Khashoggi’s murder brought renewed scrutiny not only of MBS, but also the humanitarian catastrophe in Yemen and the Trump administration’s seemingly unquestioning support for Saudi Arabia – in large part due to the strong relationship between Trump adviser Jared Kushner and the Saudi crown prince.

Meanwhile, in Yemen, as of November 2018, Human Rights Watch reported more than 6,800 civilians had been killed. And the United States, in the words of the congressional resolution, played a role in those deaths – providing “aerial refueling and targeting assistance” to the Saudis.

Trump’s veto statement called this resolution “an unnecessary, dangerous attempt to weaken my constitutional authorities.” Assuming that there are no major defections in the vote, there are not enough votes to override the veto.

But that doesn’t mean Trump has necessarily won this battle. Congress has standing to take the President to court for violating the War Powers Resolution, and a court decision could have significant ramifications for US foreign policy.

Presumably, the case would reach the Supreme Court, and if the court decides that the law is unconstitutional, it would remove one of the very few checks on the President’s ability to engage “in hostilities outside the territory of the United States.” Congress does have some checks on the President’s power in this regard, but those checks are, in practice, limited. Congress has the power to declare war, but the United States has only fought five declared wars – and none since World War II. And Congress controls the “purse strings,” but while a few progressives and libertarians might jump at the chance to cut funding for the troops, most congressmen do not want to be accused of “failing to support our troops” by not authorizing military funding.

If the court decides that the law is constitutional, then the outcome may be even more dramatic. The wars in Iraq and Afghanistan are explicitly authorized by Congress, but military actions abroad, from Somalia to Syria to Pakistan, have been justified by recent administrations as falling under the 2001 Authorization for the Use of Military Force (AUMF). This AUMF gives the President blanket authority to use force to both pursue Al Qaeda and to prevent Al Qaeda from engaging in “future acts of international terrorism against the United States,” but it is open to broad interpretation. Given a clear ruling on the WPR’s constitutionality, an assertive Congress could force the withdrawal of US forces from any country or conflict not explicitly authorized by the AUMF or any other piece of legislation.

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Of course, the War Powers Resolution need not be challenged in court. It is certainly possible that the President and Congress can reach a compromise regarding US support for Saudi Arabia. And for Congress to have standing to sue the President, it must show that an attempt to compromise had been made.

The Pentagon argues that the “US military is not engaged in hostilities in or affecting Yemen,” but acknowledges that, even if aerial refueling has ended, it is still providing “limited, non-combat support to the Saudi-led Coalition.” Thus, a compromise seems viable – Trump could agree not to resume any additional offensive military assistance, and Congress could agree to withdraw its joint resolution.

But the reality is that Congress wants to send the White House a broader message about US support for, and arms sales to, Saudi Arabia – and Trump is seemingly reluctant to take any actions that may “harm bilateral relations” with the Kingdom.