While many Americans despair of the current state of U.S. politics, most assume that our system of government and democracy itself are invulnerable to decay. Yet when we examine the past, we find that the United States has undergone repeated crises of democracy, from the earliest days of the republic to the present. In Four Threats, Suzanne Mettler and Robert C. Lieberman explore five moments in history when democracy in the U.S. was under siege: the 1790s, the Civil War, the Gilded Age, the Depression, and Watergate. These episodes risked profound - even fatal - damage to the American democratic experiment. From this history, four distinct characteristics of disruption emerge. Political polarisation, racism and nativism, economic inequality, and excessive executive power - alone or in combination - have threatened the survival of the republic, but it has survived - so far. What is unique, and alarming, about the present moment in American politics is that all four conditions exist. This convergence marks the contemporary era as a grave moment for democracy. But history provides a valuable repository from which we can draw lessons about how democracy was eventually strengthened - or weakened - in the past. By revisiting how earlier generations of Americans faced threats to the principles enshrined in the Constitution, we can see the promise and the peril that have led us to today and chart a path toward repairing our civic fabric and renewing democracy.