http://www.nytimes.com/2011/06/18/world/africa/18powers.html?_r=1&hp
pretty much sums it up
But Mr. Obama decided instead to adopt the legal analysis of several other senior members of his legal team including the White House counsel, Robert Bauer, and the State Department legal adviser, Harold H. Koh who argued that the United States militarys activities fell short of hostilities. Under that view, Mr. Obama needed no permission from Congress to continue the mission unchanged.
pretty much sums it up