The Constitution does not use the words federal or federalism. It gives Congress a set of powers and prohibits the national government, the states or both from doing some things. The Court has inferred principles of federalism from those provisions. The political science community has treated the advantages of federalism as contingent on whether federalism deepens or diffuses conflict or opens competition for power. The United States Supreme Court’s approach does neither; it has been trying to clarify and police a very different boundary. Even on its own terms, however, the Court’s justifications do not work – a problem made clearer by reference to the empirically based work of political science. The result is that the Court’s focus misses entirely the kinds of questions which might affect the security of the union or the quality of American democracy. The first section of the essay describes the Court’s efforts to create a categorical federalism and its explanations for its approach. The second section makes clear that there are alternative approaches to federalism, in the absence of which further analysis would be pointless. The third section of the essay outlines major lines of inquiry by political scientists and their conclusions. Finally, the essay compares the Court’s definitional federalism and its explanations for its approach with the concerns of political scientists. This essay concludes that the Supreme Court’s categorical federalism is at best irrelevant and at worst a barrier to contemporary conflict resolution.