Already, Harris is being described by pundits as the frontrunner in the next open Democratic primary, whether it’s in 2024 or 2028. Progressives said that means they could be locked out of the White House for more than a decade.

“We might be looking at 12 years of neoliberal power at the top of the Democratic Party because of the specter of a very young and ambitious — as most politicians are — person on the ticket,” said Norman Solomon, co-founder of the left-wing group RootsAction.org. “That’s a real fear.”

The fact that Biden is the presumptive Democratic nominee after serving as former President Barack Obama’s No. 2 — contrary to many party insiders’ low expectations for him this year — underscores the leg up that former vice presidents have in presidential primaries. And after anti-establishment Democrats and socialists watched Bernie Sanders come close to winning the nomination, that’s a serious letdown.

“The former vice president always has a major advantage so it’s definitely possible that we progressives might not have a real shot at the presidency for many years,” said an ex-senior aide to Sanders. “I think our power is going to have to come from building movements.”

The overall attitude on the left toward Harris is mixed. Compared with other politicians who were previously viewed as potential running mates to Biden, she is viewed as somewhere in the middle, neither as progressive as Bass or Elizabeth Warren nor as moderate as Rice or Amy Klobuchar.

Some liberals said Harris’ selection is a serious disappointment because of her record as a prosecutor and history of flip-flopping on "Medicare for All." Others said they're relieved Biden didn’t go with someone more centrist, and praised the fact that she is the first Black woman and South Asian American woman on a major party's presidential ticket.

“We are in the middle of the biggest protest movement in American history, which is protesting exactly the same kind of policies that, at the time, Attorney General Harris oversaw, had direct authority to change, and declined to change in meaningful ways,” said Briahna Joy Gray, Sanders' former national press secretary, referring to Harris’ time as the lead prosecutor in California. “I would like a candidate who offers big, structural change.”

Conversely, progressive consultant Rebecca Katz said that while she wanted Biden to tap Warren, “I would take Kamala Harris any day of the week over Amy Klobuchar.”

Even Berniecrats such as Gray view parts of Harris’ legislative record as more liberal than Biden’s. Harris co-sponsored Sanders’ Medicare for All bill, though she backed away from single-payer in the primary. She also endorsed the Green New Deal and a ban on fracking.

A top 2020 aide to Sanders said the Vermont senator personally gets along with Harris, and the two introduced a proposal together in May to send $2,000 monthly checks to millions of Americans during the Covid-19 pandemic. Harris has also teamed up with Rep. Alexandria Ocasio-Cortez on a climate change bill.

“I think she can be a real climate leader and look forward to working with her team on those issues," said Sean McElwee, co-founder of the progressive think tank Data for Progress.

As Biden’s running mate, however, Harris has effectively signed onto Biden's agenda. In what is possibly a demonstration of that reality, the Biden campaign declined to comment on a question about whether he backs the $2,000 monthly payments she proposed with Sanders.

At the same time, Biden said in the first event announcing Harris as his running mate on Wednesday that he asked her to be the last person in the room when he made big decisions. "To always tell me the truth, which she will. Challenge my assumptions if she disagrees. Ask the hard questions," he said.

Progressives said that selecting Harris shows that Biden is likely to govern as a moderate, despite his recent efforts to win over former Sanders voters, including by creating “unity” task forces with the Vermont senator.

“The fact that Warren and Sanders weren’t seriously considered reflects something about Joe Biden,” Bhaskar Sunkara, founder of the socialist magazine Jacobin and a former vice chairman of Democratic Socialists of America, said of Biden’s running mate selection process. “It shows that Joe Biden is going to run as Joe Biden and not pivot in any serious way to the left.”

Solomon, whose organization is spending six figures on a digital campaign to persuade swing-state progressives to back Biden, said Harris being on the ticket makes his job more difficult.

“There’s no doubt,” he said. "Harris is an archetype of apparently not having firm commitments, so it unfortunately adds to the justified cynicism that a lot of Bernie activists and overall supporters feel."

But several people on the left said the fact that Harris has changed her positions in reaction to political pressure could be an asset to them at a time when progressives are gaining power and ousting establishment Democrats in congressional primaries.

“He and Kamala Harris are not going to be able to stop these social movements that President Obama was able to placate," said David Duhalde, former political director of the Sanders-founded Our Revolution.

Jeff Weaver, Sanders’ longtime senior adviser and 2016 campaign manager, said it is significant that Harris is more liberal than Hillary Clinton’s running mate four years ago, Sen. Tim Kaine.

“This is positive movement,” he said. “If you look at what this party was and the policies that were being advocated as recently as 2016, we’ve really seen a sea change. And there is no going back.”