Bernie Sanders was once slapped by a voter for supporting Jesse Jackson's 1988 presidential campaign: book

• Sanders was slapped over his support of Jackson's 1988 presidential bid, per a forthcoming book.
• In 2020, Jackson backed the Sanders presidential campaign, citing the need for "progressive" change.

In 1988, now-independent Vermont Sen. Bernie Sanders was the mayor of Burlington, the most populous city in the state.

As one of the state's highest-profile elected officials, he threw his support behind the presidential campaign of the Rev. Jesse Jackson, the longtime civil rights leader who had unsuccessfully run for president in 1984 but made substantial gains among Black and liberal voters in his second bid for the White House in 1988.

Despite the excitement that many Democratic voters had toward Jackson's campaign, Sanders was slapped due to his support for the candidate, according to a forthcoming book by former deputy campaign manager Ari Rabin-Havt.

In the book, "The Fighting Soul: On the Road with Bernie Sanders," Rabin-Havt detailed how the Sanders campaign for months had sought Jackson's endorsement in the 2020 presidential race, and even expressed that Sanders himself sought to emulate his campaign in the mold of the pastor's famed Rainbow PUSH Coalition.

"Bernie often spoke about how he wanted to model his campaign and his movement after Jackson's Rainbow Coalition — building another working-class coalition of all races fighting for economic, racial, social, and environmental justice," Rabin-Havt said.

He continued: "As mayor of Burlington, he endorsed Jackson for president in 1988, Bernie's first real foray into Democratic Party politics. It was an incredibly risky move. Burlington is nearly all white, and his decision was not without detractors in the city. In fact, Bernie was slapped in the face at a Democratic Party gathering by a voter angered by his support for Jackson."

In March 2020, Jackson would go on to return the favor and endorse Sanders for president over former Vice President Joe Biden, who by that time had racked up significant victories in South Carolina and on Super Tuesday.

Jackson praised the grassroots foundation of the Sanders campaign in a tweet at the time.

"We look to our youth for energy, expansion and inclusion which leads to growth," he wrote. "The youth that come to these rallies represent hope, healing and promise for our nation. It's a joy to 'feel the Bern' with Bernie. Keep Hope Alive!"

Rabin-Havt relayed how moved Sanders was by the show of support, reflecting on the interactions between the two men, who had each spent decades in public life.

"I watched Bernie do something I had never seen him do before: he prayed. Here were two men who had spent their lives fighting for change, who had worked together for more than thirty years and were united once more," he wrote.

At a rally in Grand Rapids, Mich., Rabin-Havt then described how Jackson rooted his endorsement in a desire to see progressive change.

"With the exception of Native Americans, African Americans are the people who are most behind socially and economically in the United States and our needs are not moderate," Jackson told the crowd. "A people far behind cannot catch up choosing the most moderate path."

He added: "The most progressive social and economic path gives us the best chance to catch up, and Senator Bernie Sanders represents the most progressive path. That's why I choose to endorse him today."

While Sanders went on the lose the Democratic Party nomination to Biden — who eventually won the presidency that November — the ideas that sprang from the senator's campaign continue to motivate his most fervent supporters.