All three presidents since 9/11 have made innovative use of the 2001 AUMF to justify military action with only the most tenuous connection to 9/11 or al-Qaida. Barack Obama made some halfhearted attempts to repeal the law, but also used it to attack ISIS—a group that didn’t exist on Sept. 11, 2001, and opposes al-Qaida.
The AUMF is not the only tool expanding executive war powers. To justify missile strikes against Syria in 2018, the Trump administration cited Obama’s Office of Legal Counsel’s argument for the legality of the 2011 intervention in Libya: that “constrained and limited operations” did not constitute hostilities under the War Powers Resolution, and therefore do not require congressional authorization. As I wrote when Trump was considering military action against Iran last summer, it’s easy to imagine such “limited” strikes being justified the same way. (In the Soleimani case, Trump didn’t even inform congressional leaders, much less seek authorization, though Sen. Lindsey Graham says he was apparently filled in.)
Congress deserves fault for failing to exercise oversight and letting war powers expand to this degree, and the situation seems unlikely to improve any time soon. Sen. Tim Kaine, a longtime critic of executive power, says he will introduce a new war powers resolution to force a debate on hostilities with Iran, but it’s unlikely to pass in a Republican-controlled Senate. Meaningful war powers reform will require members of Congress who are willing to limit the powers of their own party’s president.