Congress’s most solemn constitutional duty is to determine whether, where, and against whom the United States will engage in war. Yet for far too long, legislators have ceded that responsibility to the executive branch, allowing multiple administrations to use the 2001 Authorization for the Use of Military Force (AUMF) as a blank check to wage war whenever and wherever the president decides. As Congress determines how to respond to growing demands for a new AUMF, it should beware of proposals that would institutionalize mission creep by surrendering more authority to the executive branch. Instead, Congress should repeal—and not replace—the 2001 AUMF.