A few years ago, when President Barack Obama unilaterally decided to intervene in Libya's civil war, he argued that he did not need approval from Congress because bombing military targets did not constitute "hostilities" under the War Powers Resolution. That argument was so laughable that it was rejected even by the war's supporters in Congress and the press, not to mention Obama's own Office of Legal Counsel.
But that's not how Obama is approaching ISIS. Obama claims Congress already declared war on ISIS, although it surely did not realize it was doing that. Thirteen years ago, the president notes, Congress authorized George W. Bush "to use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons." Jacob Sullum explains why we shouldn't buy the president's excuses for waging war without congressional approval.