... Do we need to banish history from our public life? Of course not. But we ought to think more carefully about how we put it to use. Appeals to the past are most valuable, and do most to strengthen our democratic culture, when they help us see more potential futures: by showing events to be contingent and complex, turning us away from simplistic models and easy answers, and reminding us of the terrific, terrifying creativity that drives human behavior. In practice, that means we should spend less time trying to find the perfect single equivalence between Trump and politicians past and more time reflecting on broader patterns. More than particular historical analogies, we need historical thinking.

We might start by considering how deeply language matters, how the words we use set the boundaries of political action. In medieval Europe, anti-Semitic rhetoric preached from pulpits led to real, bone-breaking violence against Jews. Crude sexual insinuations published by the French gutter press in the 1780s steadily corroded the political conventions shielding Louis XVI and Marie Antoinette, making it possible for their subjects to imagine both revolution and execution. Germans supported Hitler in part because Nazism had become salonfähig, the socially acceptable stuff of polite conversation.

When Trump mocks the disabled or wishes that he could assault protesters or predicts riots should he be denied the nomination, he widens our shared sense of what is politically possible to think, say, and do. Here the past offers not a script so much as a crucial, destabilizing insight: Words, especially words uttered in public, can have incantatory power. They can summon demons.

Mercenary and disinterested, history owes nothing to our better angels. It suggests that rules can, in fact, be broken. Systems do fail. Consider, for instance, the confidence of European leaders in 1913, men who would have chortled at the suggestion that their stable geopolitical order could ever collapse. A century later, we still remember the millions of men killed at Passchendaele, Vimy Ridge, and the Somme.

The Weimar Republic can be useful for the same reason: not for breezily labeling Trump an American Hitler, but to remind us more generally that political order can be remarkably fragile, civilization only skin-deep. After all, despite volatile economic conditions and the lingering trauma of wartime defeat, Germans in the 1920s lived under the most progressive constitution in the world: a radical democratic system of proportional representation, equal rights for women, and a guaranteed right to housing. Political disagreements worsened and polarization increased, but Germans had no reason to doubt that they lived in a modern, civilized country. It took only a few elections for the land of Beethoven and Goethe to succumb to its darkest instincts. Sheer disbelief kept many Germans from emigrating when they had the chance.

The past warns us that systems work until they don’t. Watching Trump prepare to seize the Republican nomination, it’s easy to surrender to a kind of civic paralysis that’s equal parts horror and glee. We should bear in mind, however, that this election is under no obligation to settle out safely. Political orders do not automatically sustain themselves. ...