"[T]he war power of the federal government is not created by the emergency of war, but it is a power given to meet that emergency. It is a power to wage war sucessfully, and thus it permits the harnessing of the entire energies of the people in a supreme co-operative effort to preserve the nation. But even the war power does not remove constitutional limitations safeguarding essential liberties. When the provisions of the Constitution, in grant or restriction, are specific, so particularized as not to admit of construction, no question is presented. Thus, emergency would not permit a state to have more than two Senators in the Congress, or permit the election of President by a general popular vote without regard to the number of electors to which the States are respectively entitled, or permit the States to ‘coin money’ or to ‘make anything but gold and silver coin a tender in payment of debts.’"