With Paul Pierson, I am completing a book manuscript, Madison Upside Down: The Rise of Nationalized Polarization and the Crisis of the American Constitutional Order. We argue that the particular characteristics of contemporary polarization in the United States are quite different from those experienced in earlier polarized periods in American political history. Particularly important has been the nationalization of mediating institutions, including state political parties, organized interests, and the media. This unprecedented configuration, in which polarized parties operate within a nationalized polity, generates acute challenges – ones that the American constitutional system was intended to prevent, and that it is poorly equipped to manage. We lay out the basic argument in a recent article in the Annual Review of Political Science ("Madison’s Constitution Under Stress: A Developmental Analysis of Political Polarization").