“The kind of federalism the founders espoused was not a freewheeling endorsement of state sovereignty — they had seen how dreadful the results of that might be — but a federalism that restrained power where they had seen its worst abuses: in the states. As Hamilton would write in Federalist 15, “[w]hy has government been instituted at all? Because the passions of men will not conform to the dictates of reason and justice, without constraint.” It is such constraint that requires not solely federalism, but a nation.”