A recent Radiolab episode, "60 Words", investigates exactly this question, among other things. There is a kill list, and decisions about who is or is not on th

A recent Radiolab episode, "60 Words", investigates exactly this question, among other things. There is a kill list, and decisions about who is or is not on that list are made by non-elected officials. Worse still, the Congressional oversight committee whose job is ostensibly to oversee this sort of thing apparently did not even know about the existence of the list until 2013, at which point the list had probably existed for around a dozen years.