Bernie Sanders, the self-described democratic socialist Senator from Vermont, is faring surprisingly well in the early days of the 2016 Democratic primary. Sanders’s poll numbers continue to improve against Hillary Clinton, and his campaign rallies have drawn sizeable crowds.

Sanders’s political fastball is a critique of the disparity of wealth and income between top earners and the rest of the American people. The unpolished Brooklynite turned Vermonter has promised to “wage moral and political war against wealth and income inequality in America, the worst in the industrialized world.” His means to this end include a more progressive income tax, further healthcare reform, encouragement for worker cooperatives, and federal investment in infrastructure. From a perch in the Senate’s financial services committee, Sanders can be found excoriating America’s billionaire class and its influence over America’s economy and political system.

The newfound appeal of Sanders’s economic populism recalls the last time a socialist candidate for president had even modest success with national politics. In 1912, socialist labor organizer Eugene Debs won roughly six percent of the popular vote, amounting to nearly one million votes in total. This might not seem impressive to contemporary ears, but Deb’s vote haul remains the closest a politician of the radical left has ever come to obtaining a seat in the Oval Office.

Debs’s story serves as a reminder that Americans only seriously flirt with the politics of the socialist left during eras defined by stark inequalities of wealth and income. The last of these, the period between the late nineteenth and early twentieth centuries, was – like our own – characterized by labor conflict and growing corporate power in an increasingly integrated global economy.

Debs was born in Terra Haute, Indiana in 1855, and spent his teenage years working for railroad companies, the largest business corporations of their day. An engine man on freight trains by the time he was sixteen, Debs quickly became a skilled union organizer and political orator. Like unionists across the industrialized world, he campaigned for causes such as the eight-hour working day and the abolition of child labor.

Debs did not begin his career as a socialist; he became one after his own confrontations with corporate power, above all during the Pullman strike of 1894.

In 1893, Debs left the Brotherhood of Locomotive Firemen, a trade-specific union, to form the American Railway Union (ARU), an organization open to all white railroad workers, not just those with specific craft skills. (The ARU barred entry to African-Americans.) Debs and his peers thought these “industrial unions” were essential tools for workers if they ever hoped to counterbalance the power of the railroad companies, which were national – and even international – in scope. These corporations owned track spanning the continent, coordinated from offices in New York or Boston, courted influence in Washington, and counted bondholders and shareholders abroad, especially German and English investors.

Debs and the ARU leapt into action in 1894 in solidarity with striking railcar assembly workers in a Chicago suburb. The workers were employees of the Pullman Palace Car Company and lived in George Pullman’s company town. The firm owned all shops and residential real estate in Pullman, in addition to its factory premises and machinery. When the company reduced hourly wages by twenty-five percent during the financial crisis of 1893, but refused to reduce prices or rents, the workers struck.

At first, Debs instructed ARU members to refuse to handle any trains with Pullman cars in tow. But when the railroads began to dismiss workers who refused to handle such trains, Debs called a general strike that paralyzed America’s national railroad network.

The ARU held out for a time, but the courts and the military moved to crush the action, a tactic that would speed Debs’s conversion to socialism. Attorney General Richard Olney slapped the ARU with an injunction: move the trains or face jail time. When ARU members still refused to handle the trains, President Grover Cleveland deployed troops to railroad depots to break the strike with hooves, bullets, and bayonets. They threw Debs in jail for defying the injunction.

In his cell, Debs began to reflect on the problems confronting industrial workers. He read works by European socialists who advocated not just rights and protections for workers but urged laborers to seize the means of production – as well as the machinery of state – to use industrial output for social utility rather than private profit.

Remembering the Pullman episode years later, Debs recalled that it was “in the gleam of every bayonet [that] the class struggle was revealed [to him].” “The American Railway Union was defeated but not conquered,” he asserted, “[it] lives and pulsates in the Socialist movement…its defeat but blazed the way to economic freedom and hastened the dawn of human brotherhood.”

Eugene V. Debs giving a speech from the back of a train. (NYPL Digital Collections)

After Debs was released from prison, he ran for president five times, always on the ticket of the Socialist Party of America. His socialist critique of inequality struck a chord with poor white workers and tenant farmers in the South and West, especially oil field workers, timber hands, and miners. On the stump Debs opposed “a social order in which it is possible for one man who does absolutely nothing that is useful to amass a fortune of hundreds of millions of dollars while millions of men and women who work all the days of their lives secure barely enough for a wretched existence.” His villains were the Carnegies, the Rockefellers, and other prominent families of the American Gilded Age.

Historical data on wealth and income today correspond with Debs’s image of a stratified America during the early twentieth century. In fact, ownership of national wealth (stocks, bonds, real estate, and so forth) has never been more concentrated in American history. The data on income, while less complete, suggest similar levels of stratification. The early twentieth century marked the culmination of wealth and income inequalities that had grown steadily during the post-Civil War era, as America became an urban, industrial nation.

In the same way that Bernie Sanders’s popularity represents the growing importance of wealth and poverty as flashpoints in American politics, so too did Debs’s popularity in his own day.

Despite his modest success in 1912, however, Debs cut a sad figure in later years. He was imprisoned briefly during World War I for opposing America’s involvement in the war, and he was forced to run his 1920 campaign from jail. During the glitzy boom years of the 1920s, Debs’s message fell on deaf ears. In his USA trilogy, the novelist John Dos Passos characterized the aging socialist as little but an “old kindly uncle,” elegiacally smoking cigars on his porch in Terra Haute.

Eugene Debs died in 1926, three years before the onset of the Great Depression.

While Bernie Sanders’s twenty-first century socialism is markedly different than the socialism of Debs, Sanders remains comfortable casting himself in Debs’s image. Sanders produced a documentary on Debs in 1979, and he keeps a poster of the old socialist on the wall of his congressional offices.

Sanders might have spent his formative years organizing for African-American civil rights, not unionizing railroad workers; and he might consider himself an advocate for America’s middle class, not Debs’s industrial proletariat. Still, it is hard not to hear echoes of Debs’s stump speeches in the Sanders campaign of 2015.