Before Bernie Sanders, before Zohran Mamdani, America’s favorite socialist was Eugene Debs.

In 1912, some 1,200 Socialists held elected office across the United States. Wisconsin had a Socialist congressman in Washington, and ministers in Oklahoma preached the gospel of “Christian socialism” at revival-style gatherings come summertime. The leader of this vibrant movement? One Eugene V. Debs—part working-class agitator, part radical prophet, a man who made it feel like being an American and a socialist was the most natural thing in the world.

Even opponents would describe Debs as Christlike. Born in Indiana in 1855, he’d dropped out of school at fourteen to work on the railroad. Elected to the state legislature in his twenties, he’d seemed a rising star in the Democratic Party: an optimistic moderate who urged respectability and compromise.

But this was the Gilded Age: an era of corporate tycoons and outrageous sums of money in politics, of grueling hours and few rights for workers (if any). And when, in 1894, the president sent in thousands of troops to break a nationwide railroad strike Debs helped organize, Debs was radicalized. He emerged from a six-month prison sentence as a crusader, a stirring orator who would soon see all forms of unaccountable power—rich over poor, men over women, white over Black, colonizer over colonized—as poisonous to human freedom.

Cofounding the Socialist Party of America, Debs would run for president five times and spend the rest of his life convincing ordinary workers that, together, they could create a political movement strong enough to transform the world. It wouldn’t be easy. He would suffer from chronic illness, lose friends and enrage allies, risk his marriage to a woman he loved, and receive a decade-long prison sentence for opposing World War I. And yet, countless Americans—not just in his lifetime, but in ours—would heed Debs’s righteous call for human solidarity. When Debs ran for president in 1920 from behind bars, he received almost a million votes.

A rousing, poignant, intimately human tale of struggle against the odds, American Socialist is a stunning portrait of one man’s radicalization—and of the country he radicalized in turn. It’s a story that speaks powerfully to our own Gilded Age, when the very wealthy again rule America’s political and economic life and millions are looking for an alternative.