The Vermont senator concluded a two-part launch in the Windy City, harking back to his student days in the civil rights era

In the city that inspired his political activism, Bernie Sanders concluded a two-part presidential campaign launch with a rare personal anecdote: as a college student in Chicago, he was arrested during a civil rights protest against segregation of public schools.

Before a crowd of 12,500 at the Navy Pier’s Festival Hall on Sunday night, Sanders recalled that in the 1960s, school officials in Chicago set up portable trailers for black students to keep them from attending white schools.

“One day, many of us went to the spot where they planned to put the trailers,” Sanders said. “We were corralled by a police line and told not to cross that line.

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“Well, some of us did cross that line!”

An exuberant crowd roared in applause.

As Sanders embarks on a second bid for the White House to, as he says, “finish what we started”, the 77-year-old democratic socialist is attempting to build a new kind of campaign that avoids a key weakness of his 2016 run by expanding his appeal to non-white voters.

At rallies in his Brooklyn, where he was born and raised, and in Chicago, where he graduated from college in June 1964, Sanders refreshed his now-familiar stump speech with details of his biography. The embrace of what one ally described as the “origin story of a political revolutionary” is part of a new approach his advisers and aides hope will help him connect with voters as he competes in a historically diverse field, led by women and minority candidates.

He told the audience on Sunday that his four years as a student activist were “an extraordinary moment in my life and very much shaped my world view and what I wanted to do”.

“The reason I tell you all of this is because my activities here in Chicago taught me a very important lesson,” he continued. “And that is that whether it is the struggle against corporate greed, racism, sexism, or homophobia, environmental devastation, or war and militarism, real change never takes place from the top on down. It always takes place from the bottom on up.”

In the weekend speeches, his key policy planks remained: Medicare for All, tuition-free public college and a $15 minimum wage. But in the middle of his remarks, he pivoted to offer a glimpse of the personal experiences that helped to shape them.

“You deserve to know where I come from, because family history obviously heavily influences the values that we develop as adults,” he said in Brooklyn.

The race for the party’s nomination has already attracted more than a dozen candidates and several more big names are weighing bids, including former vice-president Joe Biden, former Texas congressman Beto O’Rourke and billionaire philanthropist Michael Bloomberg. The field is dominated by women and minorities, such as Senators Elizabeth Warren and Kamala Harris, who have weaved their biographies into campaign narratives.

Since launching his campaign last month, Sanders has indicated that he is trying to remedy the shortcomings of his first campaign.

In 2016, the Vermont independent struggled to win over African Americans and other minority voters. But since losing to Hillary Clinton, Sanders has worked to strengthen ties with the black community, making several visits to the important primary state of South Carolina and working with minority organizers and activists in Mississippi and California.

In Chicago, the senator attempted to reframe his economic message to address what he called “the disparity within the disparity”: the racial wealth gap, the higher rate of infant and maternal mortality in black communities, and discrimination in the criminal justice system.

Facebook Twitter Pinterest Supporters wait for Bernie Sanders in Chicago. Photograph: Nam Y Huh/AP

He repeated the names of the victims of high-profile officer-involved deaths: Laquan McDonald, Sandra Bland, Michael Brown, Rekia Boyd, Eric Garner, Walter Scott, Freddie Gray, Jessica Hernandez, Tamir Rice, Jonathan Ferrell, Oscar Grant and Antonio Zambrano-Montes.

“People of color killed by the police who should be alive today,” he said.

Before speaking in Chicago on Sunday, he joined Clinton at the annual Martin and Coretta King unity breakfast in Selma, Alabama. The New Jersey senator Cory Booker, who is also seeking the Democratic nomination for president, and Ohio senator Sherrod Brown, who is considering a run, also spoke at the event commemorating the 1965 Bloody Sunday civil rights march.

Yet Sanders continues to face criticism for the way his speaks about race and racism – and that his economic-focused message is out of step with the current political moment that seeks to elevate women and minority candidates.

Acknowledging recently that his 2016 campaign was “too white” and “too male”, Sanders has sought to build an operation that reflects the diversity of the Democratic party. His 2020 effort will be led by Faiz Shakir, the first Muslim campaign manager of a major US presidential candidate. Co-chairs include three people of color: Turner, California congressman Ro Khanna and San Juan mayor Carmen Yulín Cruz.

He has also sought to address criticism of his campaign’s handling of sexual misconduct allegations in 2016 by instituting mandatory training and strict reporting guidelines.

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“History defines him,” Nina Turner, a former Ohio state senator who is a co-chair of Sanders’ campaign, said in Brooklyn. “But it’s not just about what he did in the 60s and the 80s and the 90s, it is about what he is doing right now.”

By sticking by Sanders 2016 playbook – big rallies and small donors – his first two weeks as a candidate served as a persuasive rejoinder to those who speculated that he would struggle to hold on to his supporters in a changed political landscape.

He has raised more than $10m in the first six days after he launched his campaign from a loyal base of supporters contributing as little as $3; and the twin rallies in Brooklyn and Chicago collectively drew more than 25,000 people.

This week Sanders will visit Iowa, where he battled Clinton to a near tie in 2016. It is there, in less than one year, that voters will have the first say on whether his unlikely political career, that the senator traced back to his upbringing in a rent-controlled apartment in Brooklyn, leads to the White House.