Sen. Bernie Sanders isn’t going to soften his views just because some moderates are lining up behind former Vice President Joe Biden after his landslide win in the South Carolina Democratic presidential primary and Pete Buttigieg’s supporters are suddenly up for grabs.

Sanders told The Chronicle on Sunday that he won’t choose a running mate who doesn’t support his signature issue, Medicare for All, a government-run single-payer health system that would require Americans to give up their private health insurance.

Polls indicate that many Democrats prefer to build on the Affordable Care Act rather than replace their private insurance with a single-payer plan. That doesn’t faze Sanders.

“We will pick somebody who knows the experience of working families in this country, who has a history of fighting for those families, and somebody whose politics are similar to mine,” Sanders told The Chronicle in an interview before taking the stage at a rally in a San Jose convention center, during which the news broke that Buttigieg was ending his campaign.

Sanders came to California a day after his first clear-cut loss of the 2020 election season, as Biden easily won South Carolina’s Democratic primary. Polls still show Sanders far ahead in California’s primary, the biggest single prize among 14 states voting on Super Tuesday.

With Buttigieg, the centrist former mayor of South Bend, Ind., having pulled out, the race is reshaping into a contest between moderates Biden and former New York Mayor Mike Bloomberg, and progressives Sanders and Massachusetts Sen. Elizabeth Warren. Minnesota Sen. Amy Klobuchar is barely a factor.

Sanders didn’t back off of any of his signature plans Sunday in San Jose, and he railed against the “Democratic establishment” that he said is trying to subvert his candidacy.

“I am here to ask you to help us change the political culture in America,” Sanders said.

The Vermont senator could grab the inside track to the nomination with a strong performance on Tuesday. In addition to being well ahead in California, he has a lead in the second-biggest Super Tuesday state, Texas.

But even a strong showing might not be enough to propel Sanders toward the 1,991 delegates he needs to secure the nomination in July. If none of the five remaining candidates has a majority going into the convention in Milwaukee, a winner might not emerge on the first ballot. On subsequent ballots, Democratic superdelegates — who are mostly elected officials and are not pledged to any candidate — would be allowed to vote.

Sanders sounded a warning against the party trying to deny him the nomination if he comes to Milwaukee with a plurality of pledged delegates.

“I think that would look terrible, and I think that would lay the groundwork for a Trump victory,” Sanders said in the interview. “It would reflect on the Democratic Party in a very, very terrible way.”

The South Carolina results revealed a potential weakness for Sanders beyond that state. He received only 13% of the African American vote in South Carolina, far behind Biden’s 61%, exit polls showed.

Sanders, however, said he wasn’t concerned. He attributed Biden’s dominance among black voters to the endorsement he received from South Carolina Rep. Jim Clyburn, the No. 3 Democrat in the House and an influential figure in the state.

“Clyburn played a very significant role,” Sanders said. But, he added, “there is a difference in how African Americans vote in California, Michigan or North Carolina.”

Sanders is the favorite of 38% of African Americans likely to vote in California’s Democratic primary, while Biden is backed by only 10%, according to a Berkeley IGS Poll released last week. That’s symptomatic of Biden’s bigger problem in California, where all recent polls show him trailing Sanders by double digits.

But even as he has built his lead, Sanders has heard concerns. One Democrat who flipped a GOP-held House seat in 2018, Orange County Rep. Harley Rouda, said last week, “I’m a little concerned that anybody that far left is going to help me in my district — unless we can overcome the votes lost by additional ones he can bring in.”

“I’ve heard about that,” Sanders said wryly Sunday. Again, he was unmoved.

“Democrats win elections when voter turnout is high,” he said. “Does anyone really think that a Biden candidacy will create the kind of energy and excitement we need to significantly increase the voter turnout?”

Sanders predicted that President Trump would easily beat Biden in battleground Midwestern states for supporting “disastrous” trade deals like the North American Free Trade Agreement.

“What do you think Trump will do with him in Michigan and Pennsylvania and Wisconsin?” Sanders said. “He’ll decimate him on that issue.”

John Sepassi, a 29-year-old San Francisco resident who attended the San Jose rally, said he likes Sanders’ “crazy progressive ideas.” The tech worker thinks Sanders will have trouble getting some of those ideas through Congress should he be elected, but said he is drawn to his vision and idealism regardless.

Sanders’ plans “are going in the direction I think the country should go,” Sepassi said.

He said it would be unlike Sanders, who has remained consistent throughout his career, to temper his most progressive ideas now to attract moderate voters.

In interviews Sunday, Biden called that a weakness, saying Sanders is too far left to be electable.

Americans “are not looking for revolution; they are looking for results,” Biden said on NBC’s “Meet the Press.”

But Sanders supporters in San Jose like Patrick Cote, a 39-year-old Sacramento resident, said it would be a mistake for Sanders to change. “He’s starting from a position of strength with the most leverage,” Cote said.

Eusbaldo Arenas, 24, said he is leaning heavily toward voting for Sanders. He likes that the candidate wants to bring “revolutionary” ideas to the country, and said Sanders’ consistency is a huge appeal.

“That’s always something that you want to see in a politician ... sticking their ground,” Arenas said. “It just makes you feel like you got someone there for you.”

Joe Garofoli is The San Francisco Chronicle’s senior political writer, and Anna Bauman is a Chronicle staff writer. Email: jgarofoli@sfchronicle.com, anna.bauman@sfchronicle.com Twitter: @joegarofoli, @abauman2