Democratic presidential candidate, Sen. Bernie Sanders, I-Vt. looking badass during a speech at Liberty University in Lynchburg, Va., Monday, Sept. 14, 2015. AP Photo/Steve Helber In 1979, before Bernie Sanders was a surging Democratic presidential candidate, before he served in Congress for 25 years, and before he became one of the biggest voices against inequality in the US, he made a spoken-word documentary.

It was his only film, but that documentary — a biographical portrait of Eugene Victor Debs and an endorsement of his socialist politics — reveals a lot about Sanders' politics today.

Sanders wrote, directed, and lent his voice for Debs' dialogue in "Eugene Debs: Trade Unionist, Socialist, Revolutionary" while he was working at the American People's Historical Society, a small company that made political documentaries.

Watching the documentary 36 years later, it's not hard to understand why Sanders found Debs such a powerful subject. The story of Debs' rise is extraordinary, and the two politicians share the same signature issue: inequality.

Debs became involved in union causes after he got into politics in 1884 as an Illinois state legislator, and was eventually jailed for six months for defying a court order to end a railway-workers strike that he had organized. In jail, Debs read communist and socialist literature, and emerged as a "radical socialist" — to use Sanders' words — bent on ending global capitalism and representing the working class.

When he arrived back home in Chicago, he was greeted by a crowd of over 100,000 people. With that support, Debs founded a string of socialist political parties and ran for president five times. He never came close to winning, but he amassed a massive following. He won 6% of the vote in 1912, his third time running for president.

Sanders had initially wanted to hire a professional actor to provide Debs' voice, but plans fell through, according to Mother Jones, so he went ahead and provided the voice himself. Listening to Sanders replicate Debs' speeches is, in some cases, not too different from listening to what Sanders is saying now in his own political speeches.

Sanders' big issue is wealth inequality. As a democratic-socialist, he wants to change the fact that a small number of people control an enormous amount of the country's wealth. As he wrote for the documentary:

Why haven't they told you about Gene Debs and the ideas he fought for? The answer is simple. More than a half century after his death the handful of people who own and control this country — including the mass media and the educational system — still regard Debs and his ideas as dangerous, as a threat to their stability and class rule, and as someone best forgotten about. ... Eugene V. Debs was a socialist, a revolutionary and probably the most effective and popular leader that the American working class has ever had.

In his presidential campaign, Sanders appears uninterested in gaining the support of elites. His campaign, like Debs', is based on the idea that the economic elite are doing too well while the working class is suffering. In his narrative of American politics, the working class and the elites are pitted against each other, and Sanders and Debs are in support of the working class.

The cover of the liner notes for Bernie Sanders' documentary about Eugene V. Debs. Smithsonian Center for Folklife and Cultural Heritage

In the documentary, Sanders identifies Debs as a symbol for the "international" working class, not just the American one. In that context, he was talking about the international socialist movement. Sanders isn't a part of that — if such a thing still exists.

But in a political climate that values American exceptionalism, he defies the status quo and points to other countries for a way forward.

"Countries like Finland and Denmark and Sweden are much more homogeneous than we are," Sanders recently told CNN, in defense of his Socialist label. "They are much smaller than we are, but there are lessons that we can learn."

Sanders and Debs understood the value of rallying the grassroots for their causes. It's partially a matter of principle, because the grassroots are the people they represent, but it's also an issue of political clout. When Debs was building the Socialist Party, he drew crowds of tens of thousands at his rallies — just as Sanders is doing at his presidential rallies.

Sanders is not nearly as much of a radical as Debs was. Much of him quoting Debs in the documentary is the sort of revolution-calling rhetoric that, should Sanders win the Democratic nomination, Republican advertisements will almost certainly quote.

Imagine how this bit of monologue, in Bernie Sanders' voice, could be used in an ad against him:

Let no one charge that socialists have arrayed class against class in this struggle. That has been done long since in the evolution of capitalist society. ... One class is small and rich and the other large and poor. One wants more profit and the other more wages. One consists of capitalists and the other of workers. There can be no peace and good will between these essentially antagonistic economic classes. Nor can the class conflict be covered up or smoothed over.

And they do have deep political differences, too. Debs thought the Republican and Democratic parties were useless for the middle class — both were on the side of capitalists — and ran for president as a Socialist. Sanders is an independent politician, but joined the Democratic ticket for his presidential campaign and has pledged not to run as an independent if he loses the nomination.

Furthermore, though Sanders is a longtime supporter of unions in his political life, he was never a union organizer. Debs was more of an outsider than Sanders ever was, spending his life organizing unions and leading a political movement without ever holding national political office.

There's no doubt that Sanders and Debs are part of the same intellectual tradition of socialism in America, and despite their differences in substance, it's there in style.