With the Illinois Democratic presidential primary coming Tuesday, Bernie Sanders will travel to Chicago this weekend to sit down for a one-on-one interview with the Rev. Jesse Jackson at the weekly forum of Jackson’s Rainbow/PUSH Coalition.

Jackson, a two-time presidential candidate who remains a dynamic figure in progressive politics, has not endorsed a candidate in the Democratic contest between Sanders and Hillary Clinton. The veteran civil-rights and economic justice campaigner has said the remaining contenders for the party nomination are “both very progressive Democrats,” while challenging claims that Sanders cannot win with the line: “Who said Bernie couldn’t win? Who’s the ‘they’? Whoever gets the most votes wins.” After Sanders secured a surprise victory in Michigan March 8, Jackson posted a statement on Facebook that complimented Clinton while explaining that: “Faulty one-sided trade policies, bank predators, growing student loan debt, loss of jobs, urban abandonment, matter. That is why Bernie Sanders overturned the bandwagon of political expectations, pundits and polls last night. His primary win in the racially diverse state of Michigan was a stunning upset—a victory for his message of schools not jails, worker’s rights and the undemocratic dominance of Wall Street over the common people.”

The Illinois primary is one of five major contests on Tuesday, when Florida, Missouri, North Carolina and Ohio will also vote. But the session with Sanders in Chicago is not just another campaign event for Sanders. It recalls a connection between Jackson and the senator from Vermont that goes back to the 1980s, when Sanders was an ardent backer of Jackson’s campaigns for the Democratic presidential nomination.

At a time when very few white elected officials were backing Jackson’s “Rainbow Coalition” run, Sanders came forward as one of the most prominent political figures in Vermont—the mayor of Burlington, the state’s largest city, and an emerging figure in statewide politics who in 1990 would unseat the state’s Republican congressman—to endorse Jackson.

Sanders and his allies were key backers of Jackson in 1988, with the independent mayor hailing Jackson’s progressive populist economic agenda and telling the Burlington Democratic caucus: “The candidate we are supporting tonight has stood for us and fought for us for the last 25 years of his life. Along with Martin Luther King Jr., he put his life on the line so that all Americans, regardless of color, could receive their basic democratic rights…. He was there when we needed him. Our candidate has stood with the farmers being thrown off the land. He has stood with the workers on the picket lines being thrown out of their jobs. He was there when we needed him…”

Jackson won a surprise victory in the Vermont caucuses that night, despite the fact that he had no paid staff in the state. Later, he would credit Sanders, former Texas Secretary of Agriculture Jim Hightower and a handful of other white elected officials who “stepped across the color line” and backed an African-American presidential candidate.

The 1988 race had a great influence on Sanders. Years later, as the pondered a run for the presidency, Sanders spoke about Jackson’s 1988 run as a model.

When I asked him two years ago about whether he saw a connection between the campaign he was considering and Jackson’s runs, Sanders responded: “Absolutely. I think Jackson has not gotten the credit he deserves. His campaigns were revolutionary: we had an African-American minister going to states like Iowa—predominantly white states—and rallying farmers. He came to Vermont; I remember I introduced him, and we had hundreds and hundreds of people out to hear him speak in a state that was then virtually all-white. The idea of bringing together people—the Rainbow Coalition concept of whites, blacks, Hispanics, Asians, gays, and lesbians—is absolutely right, and the emphasis, in my view, can be on economic issues. I happen to believe that the frustration and disgust with the status quo is much, much higher now—much, much higher than many ‘pundits’ understand. The job right now, the main focus, is to bring people together from an economic perspective, on class lines, and talk about an America that works for the vast majority of our people and not just the top 1 percent.”