“This idea commonly goes by the name “states’ rights” these days. Its opponents have conflated it with power in state governments, and some of those opponents have been so influential that many of federalism’s friends are prone to see it that way too.1 As Jefferson and the like-minded understood it, however, it meant limitation on federal power. Insofar as the US government did not have power, they believed, that power remained in the states as distinct, preexisting political communities”