In January 1962, with protests demanding equal treatment for African-Americans sweeping the country, UChicago saw its first civil rights sit-in. Thirty-three students, most of them white, marched across the gothic campus of the University of Chicago and into the administration building where, on the fifth floor, they began an occupation outside the office of President George W. Beadle. The students, members of the Congress of Racial Equality (CORE), were demanding the university end its policy of housing segregation.

For thirteen days, the students stayed night and day in the hallway next to Beadle’s office until an interim agreement was reached. And throughout the sit-in, the CORE members were led by their president, Bernie Sanders.

Sanders hasn’t always openly touted his time as a racial justice organizer while a student in Chicago. It took the 2016 unearthing of photographs and video showing a young Sanders being arrested while protesting racial discrimination in public education for this history to become a topic of discussion during his last presidential campaign.

But Sanders’s time as a student and activist in Chicago was critical to his intellectual development and shaping his worldview, particularly the centering of conflict with the powerful as a guiding political principle. Through his involvement in racial justice and socialist organizing, Sanders began to define the political commitments that continue to animate his 2020 presidential campaign, which lands in Chicago for a mass rally today.

As Sanders told the Vermont Vanguard in 1981 of his experience in Chicago, “That was probably the major period of intellectual ferment in my life.”

After the 1962 sit-in led to an agreement with the administration, the UChicago administration agreed, as such administrations love to do, to create a committee to look into the matter. This did not resolve what Sanders at the time called “an intolerable situation when Negro and white students of the university cannot live together in university-owned apartments.”

But the protests didn’t end with the creation of the committee. Students continued to pressure the administration through demonstrations and pickets of buildings that refused to rent to African Americans.

Sanders, foreshadowing what would later become a frequent campaign talking point, took to the university paper the Maroon to impel fellow students to “discuss the failings of an economic system which, despite the great wealth of the country, does not provide adequate housing for large numbers of people.”

Following sustained protests in the summer of 1963, the efforts of Sanders and his fellow student activists paid off: UChicago relented and ended official racial segregation in private university housing.

This victory would serve as motivation for Sanders’s continued organizing around civil rights. His arrest in August 1963 while protesting segregation in Chicago Public Schools came just months after the win at UChicago, a couple miles southwest of the university at 73rd and Lowe Street in the Englewood neighborhood.

Englewood had recently undergone a demographic transformation as black families, displaced by Mayor Richard J. Daley’s construction of the Dan Ryan expressway along with racist “urban renewal” redevelopment projects, moved into the neighborhood, causing white families to flee to other parts of the city. The influx of black students soon led to an overcrowding crisis. But rather than quickly investing in constructing fully-funded school buildings, superintendent Benjamin C. Willis — then one of the highest paid public officials in the country — instead chose to set up a series of twenty-five temporary trailers, which outraged parents dubbed “Willis wagons.”

Parents saw the wagons as both inadequate and discriminatory, particularly resenting their planned placement along the side of a railroad embankment. The parents, already organized as the 71st and Stewart Parent Council, reached out to CORE, which promised to work with them to stop construction of the staging site for the Willis wagons.

It was during these protests that Bernie Sanders was arrested by Chicago police. In a photo widely circulated during his 2016 campaign, Sanders can be seen with his arms grasped tightly by officers, his light pants stained with mud and his feet chained to those of two African-American fellow protesters.

While Sanders has seemed to shrug off the importance of his arrest that day in 1963 — he once told a Time reporter in 2015, “You can go outside and get arrested, too! It’s not that hard if you put your mind to it” — his activism at the forefront of the growing civil rights movement clearly shaped his politics. Later that same month, Sanders travelled to the nation’s capital to participate in the March on Washington for Jobs and Freedom, where he watched Dr. Martin Luther King Jr. — who would become a personal idol — deliver his “I Have a Dream” speech.

Explaining his participation in the civil rights movement, Sanders later told the Burlington Free Press,

It was a question for me of just basic justice — the fact that it was not acceptable in America at that point that you had large numbers of African-Americans who couldn’t vote, who couldn’t eat in a restaurant, whose kids were going to segregated schools, who couldn’t get hotel accommodations living in segregated housing. That was clearly a major American injustice and something that had to be dealt with.

These concerns continue to inform the policies that Sanders advocates today. The Racial Justice Plan his campaign released in 2015 represents one of the most comprehensive and expansive policy platforms around fighting racial inequality ever to be released by a mainstream presidential candidate. A similar plan will almost assuredly be part of his 2020 run.

Sanders has said of his tenure at UChicago, “I received more of an education off campus than I did in the classroom.” But Sanders’s studies clearly also played a role in his intellectual development.

Previously, as was a student at Brooklyn College in his home city of New York, Sanders came across a group called the Eugene V. Debs Club. In a never-published Atlantic interview, brought to light by Sanders biographer Harry Jaffe, Sanders recounted himself responding to a club activist’s pitch, “‘What’s that? I never heard of Eugene V. Debs.’ And they said, ‘Oh we’re the local socialists,’ and I said, ‘Socialists!’ I was shocked. Not that I was against it, you understand, but I was amazed. Here were real live socialists sitting right in front of me!”

Of course, consorting with socialists would soon become less of a novelty for Sanders. After familiarizing himself with writings on the Russian Revolution and the Haymarket Massacre, as he explains in his 1997 book Outsider in the House, “I read Jefferson, Lincoln, Fromm, Dewey, Debs, Marx, Engels, Lenin, Trotsky, Freud, and Reich.”

Then, while a student in Chicago, Sanders went on to join the Young People’s Socialist League (YPSL), the youth wing of the Socialist Party. In a 2016 interview, Sanders said YPSL “helped me put two and two together. In other words, we do not like poverty, racism, war, exploitation, but what do they all have in common?”

As he told a reporter for the Los Angeles Times in 1991, “When I went to the University of Chicago, I began to understand the futility of liberalism.”

During this time Sanders also honed his political persuasion chops. As Jaffe reports in his 2015 book Why Bernie Sanders Matters, the future senator attempted to convince his Milton Friedmanite freshman roommate David Reiter “that capitalism was a failed system that oppressed the majority.” Reiter recounted to Jaffe, “[Sanders] was so sad that I just couldn’t understand what was wrong with the free market. It was more in sorrow than in anger.”

Sanders elaborated on his reasons for joining the socialists in Chicago during a 2016 town hall event with MSNBC host Chris Matthews at UChicago. “What it was to me was trying to connect the dots,” Sanders told Matthews. “To understand what money and power was about, the impact that it had on society. Why it was that we had so much — and it’s worse today than we had then — income and wealth inequality.”

During his time in Chicago, Sanders also briefly organized with the United Packinghouse Workers of America, a position that introduced him to the trade union movement.

These experiences didn’t just open Sanders’ eyes to the injustice at the heart of America’s economic system. They helped forge a political identity that would color his life from that point on — one which sees workers of all races and backgrounds pitted against those who control capital and seek to keep the current order in place.

It’s fitting that Sanders is returning to Chicago as a longtime nemesis of his and his politics is on the way out.

In September 2018, Rahm Emanuel announced he wouldn’t seek a third term as Chicago mayor. Following a time in office evinced by brutal austerity, corruption, privatization, segregated gun violence, and rampant police abuse, Emanuel — the one-time prized beacon of Third Way, Democratic centrism — has seen his political career in Chicago come to an abrupt halt.

In March 2016, ahead of the Illinois primary, Sanders made his views on Emanuel explicit: “Let me be as clear as I can be: Based on his disastrous record as mayor of the city of Chicago, I do not want Mayor Emanuel’s endorsement if I win the Democratic nomination.”

Sanders’ entry into the 2020 race shows him continuing his career-long maneuver of railing against a wealthy ruling elite while calling on his supporters to join a mass movement to challenge economic and racial inequality. But this time around he’s taken a slightly different tack, weaving more of his personal narrative into his fiery jeremiads against injustice.

As his time at UChicago shows, Bernie Sanders’ political identity as a defiant democratic socialist didn’t come out of nowhere — it was honed in Chicago.