affirm[ing]" that the authority of the President under the Authorization for Use of Military Force Against Terrorists (AUMF), a joint resolution passed in the immediate aftermath of the September 11, 2001 attacks, includes the power to detain, via the Armed Forces, any person (including U.S. citizens[21]) "who was part of or substantially supported al-Qaeda, the Taliban, or associated forces that are engaged in hostilities against the United States or its coalition partners", and anyone who commits a "belligerent act" against the U.S. or its coalition allies in aid of such enemy forces, under the law of war, "without trial, until the end of the hostilities authorized by the [AUMF]"