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 Article 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.
This Article contends that the Constitution grants Congress expansive authority to structure interstate relationships and that in wielding this inter-state authority Congress is not limited by judicial interpretations of Article IV. Rather than constituting unalterable demands of union, the antidiscrimination provisions of Article IV are best understood, like the dormant commerce clause, as constitutional default rules. These provisions are judicially enforceable against the states, but their enforceability is contingent on the absence of congressionally authorized discrimination. Congress’s power to authorize discrimination has limits; however, those limits derive not from Article IV or principles of federalism, but instead from the Fourteenth Amendment.
Constitutional text, precedent, normative and functional concerns, and history all support such congressional primacy in interstate relations. Ultimately, however, the basis for broad congressional interstate authority is constitutional structure. Most of the Article is devoted to a close analysis of these standard sources of constitutional meaning to determine the appropriate parameters of the congressional role in interstate relations. The Article closes with an examination of the practical implications of such a broad view of Congress’s powers, assessing the constitutionality of DOMA and the recently proposed Child Interstate Abortion Notification Act.