obama put in place tougher rules on drone strikes in 2013 to cut down on civilian deaths , but cia got an exemption .
president must sign off on drone strikes targeting suspects on ` kill list , ' but operations against other suspected militants do n't require his approval .
obama took ` full responsibility ' for january deaths of us hostage dr warren weinstein and italian aid worker giovanni lo porto in drone strike .
senator john mccain on sunday said drone strikes against militants on foreign soil should be run by the us military and not the cia .