this book has reminded us that American democracy is not as exceptional as we sometimes believe. There's nothing in our Constitution or our culture to immunize us against democratic breakdown. We have experienced political catastrophe before, when regional and partisan enmities so divided the nation that it collapsed into civil war. Our constitutional system recovered, and Republican and Democratic leaders developed new norms and practices that would undergird more than a century of political stability. But that stability came at the price of racial exclusion and authoritarian single-party rule in the South. It was only after 1965 that the United States fully democratized. And, paradoxically, that very process began a fundamental realignment of the American electorate that has once again left our parties deeply polarized. This polarization, deeper than at any time since the end of Reconstruction, has triggered the epidemic of norm breaking that now challenges our democracy.