Enforcing federalism is most commonly thought to involve the search for aconstitutional delegation of substantive power. Although in modern times the substantive power might be overlapping or shared authority, federalism enforcement proceeds from a determination about the site of substantive power. This conception of federalism enforcement preserves the Constitution’s commitment to fractionated authority by determining whether power is legitimately possessed. Thus we understand significant federalism disputes in our age as framed by whether Congress has the authority to enact comprehensive health care reform legislation, or whether Congresshas exceeded its authority in reenacting the Voting Rights Act’s preclearance requirements. Federalism...