Today, the words “federalism” and “originalism” are bandied about in the news almost daily, but to get at the underpinnings of these modern interpretations of constitutional law, it is essential to look at how the Constitution was being interpreted and applied during the crucial period of 1815-1861, between the end of the War of 1812 and the beginning of the Civil War. Early nineteenth-century Americans found themselves consumed by arguments about concurrent power—the areas in which the Constitution had left the line between federal and state authority unclear. The scope of specific concurrent powers became increasingly important, and controversial, in the early nineteenth century. In 1815, the most pressing political and legal issues increasingly concerned situations in which multiple layers of governmental power overlapped—and the Constitution provided no clear delineation. Moreover, the choice of which level of government regulated each subject had dramatic consequences for the policy that resulted. To explore this topic is today’s guest, Alison LaCroix, author of “The Interbellum Constitution: Union, Commerce, and Slavery in the Age of Federalisms.” We see just how deeply these constitutional questions dominated the discourse of the time.