Almost all of the federal government's actions against terrorism — from drone strikes to the prison at Guantanamo Bay — are authorized by a single law: the Authorization for Use of Military Force.
Congress passed it just after the terrorist attacks of Sept. 11, 2001. Now, President Obama says he wants to revise the law, and ultimately repeal it.
The AUMF is one of the most unusual laws Congress has passed this century. It's less than a page long. The vote was nearly unanimous.