Sen. Bernie Sanders, the Vermont independent who pulled the Democratic presidential field to the left on health care and college affordability, suspended his presidential campaign Wednesday, saying his path to the nomination is “just not there.”

Sanders’ withdrawal from the race all but ensures that Joe Biden will be the Democratic challenger to President Trump in November. The former vice president’s first job, however, will be to win over voters who were energized by Sanders in 2016 and again this year.

Just because Sanders is out doesn’t mean his supporters will reflexively go over to Biden. Many of his California backers interviewed Wednesday said they would be more likely to fall in line if Biden supports the issues that drove Sanders’ candidacy — Medicare for All, free college tuition, the Green New Deal environmental plan — and picks a progressive running mate.

Biden will also have to work harder to connect with younger voters and Latinos, key constituencies that preferred Sanders during the campaign and whose support — and enthusiasm — are likely to be necessary for Biden to beat Trump.

An ABC News-Washington Post poll last month found only 24% of Biden’s supporters back him “very enthusiastically,” which would be the lowest mark for a Democratic nominee since Al Gore in 2000. Twice as many of those supporting Trump were “very enthusiastic” about him.

And Biden can’t afford to take Sanders voters for granted. In 2016, one in 10 Sanders primary voters — 1.5 million people — backed Trump in the general election, according to a Tufts University study.

Some asked for more detail on how Sanders primary voters behaved in general. This graphic shows this, including small % who abstained 2/n pic.twitter.com/iOjKr7eoYJ — Brian Schaffner (@b_schaffner) August 23, 2017

“Joe Biden does have to earn the votes from the Sanders wing of the Democratic Party,” said Brandon Harami, co-chair of of SF Berniecrats and a California Democratic Party delegate. “If Biden wants to earn those votes, he needs to not only embrace those policies that reflect (Sanders’) ideology, but he needs to sit down and listen to Sanders voters and Sen. Sanders himself.”

Longtime Sanders confidante RoseAnn DeMoro, former head of the National Nurses United union, told The Chronicle that “it will be a big lift to get Sanders supporters behind Biden. People really don’t like him and are angry.”

Biden praised Sanders on Wednesday for putting “income inequality, universal health care, climate change, free college (and) relieving students from the crushing debt of student loans” at the center of the Democratic campaign. And he promised to listen to Sanders’ army of backers.

“I see you, I hear you and I understand the urgency of what it is we have to get done in this country,” Biden said.

He said that “while Bernie and I may not agree on how we might get there, we agree on the ultimate goal for these issues and many more.”

The overture was a start, said R.L. Miller, who chairs the environmental caucus of the California Democratic Party and supported Sen. Elizabeth Warren in the state’s primary last month. “But Biden needs to do a lot of work at his end,” Miller said.

Biden does not support the nonbinding Green New Deal proposal, which calls for the U.S. to run on 100% renewable energy within 10 years. Unlike Sanders, Biden backs fracking, which is key to his support in battleground states such as Pennsylvania, where the industry accounts for many jobs.

“He’s been openly scornful of the Bernie folks and the Green New Deal and Medicare for All,” said Miller, founder of the Climate Hawks Vote environmental advocacy organization. “The Bernie people, particularly young voters and Latinos, don’t see anything that gets them enthused about Biden.”

Alan Minsky, executive director of Progressive Democrats of America, told The Chronicle that “of course (his group) and all the other progressive organizations will support Biden over Trump. But neither us nor Bernie himself can magically deliver the progressive vote. I do think that can be achieved by endorsing” Medicare for All.

Biden told MSNBC last month that he would probably veto a bill to have the government administer the U.S. health system, in part because of its projected cost. The nonpartisan Urban Institute estimates that a plan like what Sanders wants would increase federal spending by $34 trillion over a decade.

Sanders supporters “will also be looking to see who Biden selects as VP,” said former San Francisco Supervisor Jane Kim, who was Sanders’ political director in California.

Biden has promised to select a woman as his running mate. Some Sanders supporters warn him not to repeat what they viewed as Hillary Clinton’s 2016 mistake in picking a moderate, in her case Virginia Sen. Tim Kaine.

“If Biden picks someone Tim Kaine-ish, he will miss out on the chance to make people enthusiastic for his campaign,” said Harami of the SF Berniecrats.

Biden also will have a challenge in winning over Latino voters, who supported Sanders overwhelmingly in California and Nevada. Biden needs to build up a campaign in Latino communities, something that helped Sanders win both states’ Democratic contests.

Biden “needs to hire Latino staff at seniors levels of his campaign and build an organization in Latino communities,” said Rafael Návar, who ran Sanders’ campaign in California and New York.

Sanders indicated Wednesday that he would still be a presence in the race. He said he would remain on the ballot in the states that have yet to hold contests so he could win more delegates and “exert significant influence over the party platform.”

Then, Sanders said, “together, standing united, we will go forward to defeat Donald Trump.” He praised Biden as “a very decent man who I will work with to move our progressive ideas forward on a practical note.”

After all, Sanders told his audience, “We have never been just a campaign. We are a grassroots, multiracial, multigenerational movement which believes that real change never comes from the top on down, but always from the bottom up.”

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