Without the aid of the courts, Congress is no match for the Executive. Presidents decide, period. Congress, outgunned by the Executive and deserted by the Judiciary, goes along. The Framers would have been dismayed.
In short, the power to give or withhold a declaration of war was generally viewed by the Founders as tantamount to the power to decide whether hostilities would take place, with the well-recognized exception of defense against direct attack. This placed the real war-making power in the hands of the Congress, not the President.