The decisive test case for the separation of powers is whether members of Congress will defend their branch of government even if a president of their own party occupies the White House. Might such a willingness be brewing? A story in The Washington Post reports that several Democratic members of Congress who pushed to reclaim legislative war powers under former President Trump are persisting under President Biden. The most encouraging explanation of their intentions came from Democratic Senator Tim Kaine of Virginia, who promised “civil dialogue” with the White House on matters like repealing the post-9/11 Authorization for Use of Military Force. However, he continued, “we’re not playing ‘Mother May I.’ We’re going to do what we think is right. But we would rather do it knowing what [the White House thinks] about it.”

Biden, a staunch advocate of Congressional power as a senator, appears to be balking as president. That is to be expected, and public officials should bring different perspectives to bear when serving in different branches of government. The Madisonian point is that an official’s first loyalty should be to his or her branch rather than his or her party. The question about the AUMF is not simply its substance. Constitutionalism forces the question of authority. “How” is as important as “what.”

The post-9/11 AUMF, enacted 72 hours after the attacks and still in force almost two decades later, is a compelling reminder that Congress should be wary of surrendering power that it will need a president’s signature to reclaim. The AUMF has not only authorized enduring war in Afghanistan, it has also been put to all kinds of uses no one anticipated. Perhaps the most important lesson to be learned from this story does not derive from 9/11. It is that the AUMF for the 1991 Gulf War is still in force. People who were not yet born as of its enactment are now eligible to serve as senators. Is that degree of absurdity necessary to galvanize Congress?