Sen. Bernie Sanders is defying predictions that he would recede into the progressive fringes after his high-profile presidential run. With President Trump in the White House and Republicans in total control of Congress, some thought Sanders was too liberal to be relevant. Too quirky. Too ... Vermont.

Instead, fueled in part by the resistance to Trump, Sanders’ influence continues to grow. His proposals, which once seemed too close to the fringe, are moving closer to the mainstream, especially in California, where a single-payer health care plan has been introduced in the Legislature and a form of free college is being considered in San Jose. The grassroots opposition energy is a descendant of Sanders’ presidential campaign — some of his interviews on Facebook Live (and now a podcast) have reached 1.7 million viewers.

Next week Sanders will start touring swing states with new Democratic National Committee Chairman Tom Perez. It’s a show of unity after Sanders’ preferred candidate, Rep. Keith Ellison, D-Minn., lost the race for party chair.

“The center of gravity has definitely moved to the left since the election,” said David Mermin, a pollster and strategist at Lake Research Partners who has conducted focus groups on progressive attitudes since the election. “Of course, what’s really driving the intensity on the left is that people are scared and nervous about Trump. But there’s no question that Sanders has been influential.”

While there appears to be momentum on the progressives’ side, Sanders’ strand has had its setbacks, starting with Ellison’s loss of the DNC chairman’s race. In a nod of respect to progressive power, Perez appointed Ellison vice chairman.

While Berners batted slightly above .500 on campaigns where Sanders endorsed a candidate last year, they’re now getting traction on policy proposals the movement championed during the election.

Few pundits thought Sanders’ staples, like single-payer health care and free college tuition, resonated beyond progressive enclaves like the Bay Area. And while the senator either has introduced or will soon introduce freshened versions of those ideas in the Senate, they aren’t likely to go anywhere in the GOP-dominated Congress.

But in California, state Sen. Ricardo Lara, D-Bell Gardens (Los Angeles County), says Sanders “was definitely an influence” in Lara’s co-authoring a single-payer plan for California this month in the Legislature, according to a spokesman.

And even though San Jose Mayor Sam Liccardo supported Hillary Clinton in the Democratic primary, he tipped his cap to Sanders’ campaign for helping to mainstream the idea behind his new San Jose Promise program, which proposes to cover two years of community college costs for 800 students in his city.

“If the Bernie Sanders campaign proves to have been a gateway drug for greater societal investment in pathways to success for students living in poverty, well, then that’s a worthwhile legacy,” Liccardo said.

And while progressives have been promoting a single-payer health plan for decades — the California Legislature was the first in the nation to pass a single-payer bill, in 2006, but it was vetoed by Gov. Arnold Schwarzenegger — polling shows that the political climate now may be more accepting of the concept.

It’s another sign to Shannon Jackson, a longtime Sanders aide who is the executive director of the Sanders-inspired Our Revolution activist group, that Sanders is ahead of the curve.

“You can listen to a speech when he ran for mayor (of Burlington, Vt., in the 1980s) or when he was running for president — and he’s talking about the same things,” Jackson said. “The public has finally caught up to what he has been advocating for.”

Many of those who got swept up in the energy of Sanders’ presidential campaign have channeled their post-election frustration into working against the administration.

Strains of the Sanders campaign formula can be seen in the hundreds of anti-Trump resistance groups that have sprung up around the country. Some, like the Indivisible network that has spawned more than 5,000 chapters nationwide, have tapped into the same organizational formula the Berners did.

“You definitely see similarities in how both use a distributive organizing model where you have a central organizing body and leaders on the ground,” said Ezra Levin, executive director of Indivisible. However, he was quick to add that Indivisible members are “Bernie supporters and Hillary supporters, and people who weren’t involved in politics before.”

And while Sanders has been influential in the Trump era, social movements expert Michael Heaney cautions “not to overwrite” his influence. Sanders’ following, he said, is the latest offspring in an activist lineage stretching from the anti-globalist demonstrations of the late 1990s to the anti-Iraq War demonstrators to the Occupy Wall Street and Black Lives Matter movements of the past few years.

Plus, now that it is unlikely Sanders, 75, will run for president again, “he has a purity about him. He is sort of a savior who can rise above the politics,” said Heaney, a professor of political science at the University of Michigan and producer of the documentary “The Activists: War, Peace and Politics in the Streets.” “And since the Democrats are out of power and have no leader, he can become a symbolic leader of the left.”

Three of the 24 candidates in last week’s special congressional election in Los Angeles said Sanders inspired them to run. None, however, finished in the top two and so will not advance to the general election to replace Xavier Becerra, who resigned to become California attorney general. Sanders did not endorse a candidate.

Overall, candidates endorsed by Sanders’ post-Democratic-primary organization, Our Revolution, won 59 of the 106 races last fall.

That’s a winning record, but analysts predict some Democrats will be walking a tightrope as they begin gearing up for the 2018 midterm elections. Some Democrats will be worrying about alienating more conservative blue-collar white voters who flipped to support Trump last year, while keeping the more progressive Sanders supporters engaged.

“They want to keep the Bernie voters, so it’s important to keep alive the Bernie movement going through 2018,” said Jaime Regalado, professor emeritus of politics at California State University Los Angeles. “But at the same time they’re going to have to figure out how to get back in the game in the Midwestern states where they thought they would win.

“They need to go after both — and it is going to be a challenge,” Regalado said.

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli