The anxiety began well before the Cleveland convention, where the candidate of the “Forgotten Men,” the one who declared Americans “the greatest Race on the face of this old Earth,” seemed likely to clinch his party’s presidential nomination. Doremus Jessup, the protagonist of Sinclair Lewis’s 1935 novel “It Can’t Happen Here,” sees something dark and terrible brewing in American politics — the potential for “a real fascist dictatorship” led by the up-and-coming populist candidate Berzelius Windrip. Friends scoff at this extravagant concern. “That couldn’t happen here in America, not possibly!” they assure him. But Jessup, a small-town Vermont newspaper editor and a “mild, rather indolent and somewhat sentimental liberal,” worries about the devastation ahead. “What can I do?” he agonizes night after night. “Oh — write another editorial viewing-with-alarm, I suppose!”

When Election Day comes to pass, Jessup learns that his editorials have not done the trick. The reality of the new situation feels unspeakably awful, “like the long-dreaded passing of a friend.” Jessup faces the presidential inauguration in a state of high distress, convinced that the nation is careering toward its doom, but that nobody — least of all his fellow liberals — can do much to stop it.

“It Can’t Happen Here” is a work of dystopian fantasy, one man’s effort in the 1930s to imagine what it might look like if fascism came to America. At the time, the obvious specter was Adolf Hitler, whose rise to power in Germany provoked fears that men like the Louisiana senator Huey Long or the radio priest Charles Coughlin might accomplish a similar feat in the United States. Today, Lewis’s novel is making a comeback as an analogy for the Age of Trump. Within a week of the 2016 election, the book was reportedly sold out on Amazon.com.

At a moment when instability seems to be the only constant in American politics, “It Can’t Happen Here” offers an alluring (if terrifying) certainty: It can happen here, and what comes next will be even ghastlier than you expect. Yet the graphic horrors of Lewis’s vision also limit the book’s usefulness as a guide to our own political moment. In 1935, Lewis was trying to prevent the unthinkable: the election of a pseudo-fascist candidate to the presidency of the United States. Today’s readers, by contrast, are playing catch-up, scrambling to think through the implications of an electoral fait accompli. If Lewis’s postelection vision is what awaits us, there will be little cause for hope, or even civic engagement, in the months ahead. The only viable options will be to get out of the country — or to join an armed underground resistance.