Iv , and Interstate Relations

Article IV imposes prohibitions on interstate discrimination that are central to our status as a single nation, yet the Constitution also grants Congress broad power over interstate relations. This raises questions with respect to the scope of Congress's power over interstate relations, what is sometimes referred to as the horizontal dimension of federalism. In particular, does Congress have the power to authorize states to engage in conduct that otherwise would violate AHicle IV? These questions are of growing practical relevance, given recently enacted or proposed measures — the Defense of Marriage Act (DOMA) being the most prominent example — in which Congress has sanctioned interstate discrimination and other state measures seemingly at odds with fundamental precepts of horizontal federalism. These questions also are significant on a more conceptual level, as they force clarification of the proper relationship between Congress and the Supreme Court in horizontal federalism disputes.