Congress actually does set he law
US Constitution Article 1 Section 8:
To define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations;
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;
To provide and maintain a Navy;
To make Rules for the Government and Regulation of the land and naval Forces;
DC: The courts really have no say over Guantanamo or the American that was droned while fighting for the enemy on foreign soil. So SCOTUS would not say the CiC makes the law.