On the Constitutionality of using Blackwater (for example) to enforce US (civilian or military) laws US Constitution, Article I, section 8: Clause 1: "The Congress shall have Power.." <list of enumerated powers> Clause 11: "To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;" Constitutional meaning of the phrase "Letters Of Marque And Reprisal" [Follow Link]