If federalism was a new kind of constitutional physics, Madison was its Einstein or its Newton and he thought so.
Madison's legacy matters today more than ever. As founding genius he made the Constitution to avoid faction. Then he discovered the real world required parties — so he founded one and became a partisan. Ultimately he turned to foreign policy, seeking to establish America's place in the world without force. He almost succeeded. Harvard Law Professor Noah Feldman discusses his new biography "The Three Lives of James Madison."