"America failed the first test in November 2016, when we elected a president with a dubious allegiance to democratic norms. Donald Trump’s surprise victory was made possible not only by public disaffection but also by the Republican Party’s failure to keep an extremist demagogue within its own ranks from gaining the nomination. How serious is the threat now? Many observers take comfort in our Constitution, which was designed precisely to thwart and contain demagogues like Donald Trump. Our Madisonian system of checks and balances has endured for more than two centuries. It survived the Civil War, the Great Depression, the Cold War, and Watergate. Surely, then, it will be able to survive Trump. We are less certain. Historically, our system of checks and balances has worked pretty well—but not, or not entirely, because of the constitutional system designed by the founders. Democracies work best—and survive longer—where constitutions are reinforced by unwritten democratic norms. Two basic norms have preserved America’s checks and balances in ways we have come to take for granted: mutual toleration, or the understanding that competing parties accept one another as legitimate rivals, and forbearance, or the idea that politicians should exercise restraint in deploying their institutional prerogatives. These two norms undergirded American democracy for most of the twentieth century. Leaders of the two major parties accepted one another as legitimate and resisted the temptation to use their temporary control of institutions to maximum partisan advantage. Norms of toleration and restraint served as the soft guardrails of American democracy, helping it avoid the kind of partisan fight to the death that has destroyed democracies elsewhere in the world, including Europe in the 1930s and South America in the 1960s and 1970s. Today, however, the guardrails of American democracy are weakening. The erosion of our democratic norms began in the 1980s and 1990s and accelerated in the 2000s. By the time Barack Obama became president, many Republicans, in particular, questioned the legitimacy of their Democratic rivals and had abandoned forbearance for a strategy of winning by any means necessary. Donald Trump may have accelerated this process, but he didn’t cause it. The challenges facing American democracy run deeper. The weakening of our democratic norms is rooted in extreme partisan polarization—one that extends beyond policy differences into an existential conflict over race and culture. America’s efforts to achieve racial equality as our society grows increasingly diverse have fueled an insidious reaction and intensifying polarization. And if one thing is clear from studying breakdowns throughout history, it’s that extreme polarization can kill democracies. There are, therefore, reasons for alarm. Not only did Americans elect a demagogue in 2016, but we did so at a time when the norms that once protected our democracy were already coming unmoored. But if other countries’ experiences teach us that that polarization can kill democracies, they also teach us that breakdown is neither inevitable nor irreversible. Drawing lessons from other democracies in crisis, this book suggests strategies that citizens should, and should not, follow to defend our democracy."