Joe Biden won big endorsements this week from former President Barack Obama and Sen. Bernie Sanders, but what he really needs is more support from the people of color and young voters who backed Obama and Sanders.

Way To Win, a progressive donor group launched in San Francisco, is trying to help by spending $5 million on organizations aimed not only at turning out voters of color, but at dispelling what it calls “disinformation” about Biden in their communities, The Chronicle has learned.

The expenditure from Way to Win, which already has dropped $37 million on key congressional and legislative races, is focused on boosting digital operations and thwarting online disinformation — a nod to how the coronavirus is limiting face-to-face campaigning.

It is also a nod to a lack of enthusiasm for Biden among parts of the Democratic base. African American voters may have propelled the former vice president to victory in the primaries, but the key in the general election will be whether they turn out in large numbers, like in 2008, or in not-so-large numbers, like in 2016.

“It’s a real concern,” said Jenifer Ancona, a co-founder of Way to Win and an Oakland resident. “That is why, regardless of what happened in the primary, Democrats cannot take black voters for granted. We saw what happened with Hillary Clinton” four years ago.

Clinton rode the support of African American voters to defeat Sanders in the Democratic primaries in 2016, Ancona said, “but in the general election, she didn’t do the investment she needed to do.”

Biden has other problems. Young voters overwhelmingly lined up behind Sanders in this year’s primaries, as did Latinos. An ABC News-Washington Post poll last month found only 24% of Biden’s supporters backed him “very enthusiastically,” which would be the lowest mark for a Democratic nominee since Al Gore in 2000. Twice as many of President Trump’s supporters were “very enthusiastic” about him.

Biden’s challenge is that one of the best ways to “engage with young voters is face-to-face contact and in-person events,” said Rep. Katie Porter, D-Irvine, who endorsed Biden this month after supporting Sen. Elizabeth Warren in the primaries.

“This pandemic is going to be a challenge to reach those people,” Porter said on The Chronicle’s “It’s All Political” podcast. “I think Joe Biden has potential to connect with young people, but it will take a real effort to do so.”

It also will take a real effort for Biden to reach other voters who backed his rivals.

“It’s clear that the challenge for Biden will be among Latinos,” said Maya Gomez-O’Cadiz, deputy director of research for Hispanas Organized for Political Equality, which focuses on Latinas. “There’s little likelihood that young Latinos would vote for Trump, but the question remains whether they would come out and vote.”

One reason for the dampened enthusiasm is the amount of disinformation online aimed at African American, Latino and other non-Anglo voters, Ancona said. That is what Way to Win hopes to change by investing in grassroots organizations led by people of color.

One of the organizations Way to Win has been funding since last fall is Fight for the Base, which tries to counter online disinformation aimed at communities of color.

Those campaigns dampen potential voters’ enthusiasm by expressing support for a sympathetic issue while simultaneously “stoking their cynicism” about the electoral process, said Fight for the Base founder Andre Banks.

For example, Banks said, he often sees social-media posts about the evils of mass incarceration, “but then they will say something like, ‘Since the system is broken, voting won’t do anything to change it,’” he said.

“This is digital voter suppression,” Banks said. “We saw that strategy in 2016, and the tactic is alive and well today. In 2016, we reacted too late. We’re not going to do that this time.”

Four years ago, Trump’s campaign ran online ads recalling that Clinton used the term “super-predators” to describe young, mostly African American criminals in the 1990s. His strategy was to depress support for the Democratic nominee among African Americans, who are normally among the party’s most loyal voters.

Instead of “buying a zillion dollars worth of Facebook ads” to counter those messages, Banks said, Fight for the Base is working with organizations led by people of color and young people. The goal is for those grassroots groups to counter the misinformation through their own online networks in their own voices.

“The best way to fight disinformation is to have culturally competent content coming from trusted messengers,” Ancona said.

Still, countering that misinformation will take time and a sustained effort, said Michael Lawson, president of the Urban League of Los Angeles.

“We have to make sure that everyone in our communities understands the importance of this,” Lawson said.

Suppressing the African American vote “has been been a part of the American landscape since the emancipation,” he said. “This is just the 21st century version of it.”

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