Since President Barack Obama laid out his strategy to degrade and ultimately defeat the Islamic State of Iraq and al-Sham, or ISIS, the debate has turned to whether he has sufficient legal authority to carry out that strategy or whether he needs a new congressional authorization for this mission. This is now even more pressing as U.S. and coalition air forces began striking ISIS targets in Syria this week, expanding U.S. military action to a second country. While the Obama administration has asserted that it has sufficient legal authority for this mission, many legal scholars and some elected officials on both sides of the aisle disagree.
via Understanding Authorizations for the Use of Military Force | Center for American Progress.