Sanders himself outlined an us-vs.-them construct for the campaign at a news conference Wednesday in Burlington, Vermont, where he listed the forces stacked against him, including Wall Street and "the entire corporate establishment."

"There has been never a campaign in recent history which has taken on the entire political establishment, and that is an establishment which is working frantically to try to defeat us," he said.

"There has not been a campaign that is trying to deal with the kind of venom that we're seeing from some in the corporate media," Sanders added. "This campaign has been compared to the coronavirus on television. We have been described as the Nazi army marching across France, etc., etc. As we come into the last several months of this campaign, what I hope very much is that what we can focus on is an issue-oriented campaign, which deals with the concerns of the American people."

When asked about Bloomberg, Sanders said he had "no animus" toward the former mayor, "but this just confirms exactly what I said. It's what the media has been talking about for months. How do we stop Bernie Sanders? How do we stop a movement of working people and low-income people? How do we stop a multi-generational, multi-racial movement, which is standing up for justice?"

"We've seen, unfortunately, what kind of campaigns Bernie Sanders runs. We saw the impact that it had in 2016," Biden deputy campaign manager Kate Bedingfield told reporters.

US Rep. Cedric Richmond, a co-chair of Biden's campaign, also took issue with Sanders' characterization of Biden's victories Tuesday night, pointing to his huge margins among black voters.

"I just did not know that African Americans in the South were considered part of the establishment," the Louisiana Democrat said.

"Nobody likes him," she said of Sanders. "Nobody wants to work with him."

Among Democrats more broadly, Jen Psaki, a former Obama adviser who's now a CNN contributor, pointed out that since Clinton's defeat in 2016, there has been a much greater recognition of the power and importance of Sanders' coalition, which is why Biden has labored to strike a tone of inclusivity.

"There wasn't the same fear of (Trump) going into the White House that exists now, and that will be a big motivator that it was not four years ago," Psaki said. "There was a lack of understanding of the power of Bernie Sanders' support and the loyalty of his support. And there probably wasn't enough seriousness taken -- the need to reach out to people who felt disaffected, who didn't feel heard, who felt that their movement wasn't taken seriously and was undervalued when it shouldn't have been."

"On the flip side, the lesson has not been learned on the Bernie Sanders side, in my view. This is about addition, not subtraction," Psaki said. "And you're not going to win by alienating large swaths of Democrats out there -- people who don't feel like they want to be part of Bernie Sanders' movement, they just want to defeat Donald Trump and they want their health care protected."

A divide by age and race

Biden was also favored by older voters, while Sanders maintained his huge edge among younger voters. The former vice president carried 46% of voters 65 and older, while 14% of them supported Sanders, according to CNN's analysis of the exit polls.

Sanders' claim that he can expand the Democratic coalition by bringing out a younger, more diverse group of voters, while also activating working-class voters who have opted out of the system, so far has not come to fruition. In states like North Carolina and Massachusetts, Sanders did not do as well with non-college-educated white voters as he did four years ago. His loss in Minnesota, another state with a large working-class population where he'd hoped to do well, was also notable.

"Bernie Sanders needs to grow his support significantly to win the nomination and that begins with the African American community. If he doesn't do much better with those voters, his chances of being the nominee are awfully close to zero," said Dan Pfeiffer, a former senior adviser to Obama. "That alone will not be enough. To date, his campaign has at times given off a 'my way or the highway vibe' that has put a ceiling on his support among large swaths of the party."

The senator acknowledged on Wednesday that expanding the Democratic coalition has been hard for his campaign. As of 4 p.m. ET on Wednesday, Biden was leading Sanders in the popular vote by 900,000 ballots, depriving the senator of the argument about his people-powered campaign that he had used after losing the delegate count in Iowa to Buttigieg (but leading in the raw vote totals).

"We're making some progress, but historically everybody knows that young people do not vote in the kind of numbers that older people vote in," Sanders said. "I think that will change in the general election, but I am honest. ... We have not done as well in bringing young people into the political process. It is not easy."

He framed the newly shaped race in stark terms. The question for voters, he said, "is which side are you on?"