Following Donald Trump’s election, the 2016 British Brexit referendum, and the rise of populist authoritarianism around the globe, a wave of scholarship emerged that focused on democratic breakdown and erosion. Underpinning this literature is a fear that long-standing constitutional and democratic orthodoxies—ideas that are broadly accepted and therefore seldom questioned—are under considerable stress. This paper is a comparative constitutional study of democratic erosion in the United States. Donald Trump’s presidency was a gift to constitutionalists because it enabled them to observe the erosion of a long-standing, wealthy democracy. Prior to Donald Trump’s election, constitutionalists faced a problem. The American constitutional order differs considerably from those of its peer democracies—those democracies continuously in operation since 1950—yet all those democracies appeared to function tolerably well. That claim is no longer sustainable. The United States elected a demagogue to the presidency of the United States. Consequently, it has gone farther down the path of democratic erosion than its peer democracies. Trump- ism challenges three political-constitutionalist orthodoxies: (1) that wealthy, long- standing democracies are immune to breakdown and should resist erosion; (2) that presidentialism works well in the United States even though it has largely failed abroad; and (3) that the peculiar form constitutionalism took in the United States is the cure for the excesses of democracy.