The AUMF is the War on Terror’s key piece of legislation. The text of the law is brief, beginning with, “Whereas, on September 11, 2001, acts of treacherous violence were committed against the United States and its citizens,” and ending with an assurance that nothing in it would supersede “any requirement of the War Powers Resolution,” the 1973 law passed (over Nixon’s veto) to prevent any more Presidents from waging undeclared war, as they had for years in Korea and Vietnam. In practice, however, the main effect of the AUMF has been precisely to supersede the War Powers Resolution, which at this point may as well not exist. The AUMF frees Presidents to fight “terrorism” without having to seek Congressional approval to do so, and it frees Congress from having to take any responsibility for the moral or strategic costs of those conflicts.
A 2016 paper from the Congressional Research Service helps to illustrate the AUMF’s reach. The CRS found thirty-seven separate instances between 2001 and 2016 on which Presidents Bush and Obama cited the AUMF as authorizing them to engage in some form of military action overseas. These include: combat action against al Qaeda in Afghanistan (2001); the opening of Guantánamo, as well as foreign military training in the Philippines, Georgia, and Yemen (2002); deployment to Djibouti and “maritime interception operations on the high seas” (2003); military operations in Iraq (2004); deployment (it’s not specified where) to enhance counterterrorism capabilities of “friends and allies” (2006); airstrikes and sea-launched strikes against Somalia (2007); “working with counterterrorism partners to disrupt and degrade al Qaeda and its affiliates” (2010); the detention of some one thousand “al Qaeda, Taliban, and associated fighters,” plus the execution of a “clear-hold-build strategy” in Afghanistan (2011); “direct military action against al Qaeda in the Arabian peninsula,” including in Yemen (2012); the capture of a single member of al Qaeda in Libya (2013); and a campaign of airstrikes against the Islamic State in Iraq and Syria, the use of US armed forces to support Iraqi security forces, a series of strikes against the Khorasan group of al Qaeda in Syria, and one airstrike in Somalia (2014). 2015 saw US support for anti–al Qaeda operations in Afghanistan, US support of a Kurdish Peshmerga rescue operation in Iraq, the deployment of US forces to northern Syria, and the deployment of combat aircraft and personnel to Turkey—all authorized by the AUMF. Not that Congress has, save in a few cases, ever bothered to ask.