Florida delegate Sanjay Patel sports a “Feel The Bern jacket” in Philadelphia on Monday. (Michael Robinson-Chavez/The Washington Post)

Bernie Sanders came to Philadelphia with the primary campaign behind him, hoping to unify millions of skeptical voters behind the Democratic ticket, starting with his delegates. He gathered all of them, numbering nearly 1,900, in a crowded ballroom Monday and told them point-blank that “we’ve got to elect Hillary Clinton.”

What he heard back was a chorus of boos, from delegates still not ready to support the likely Democratic nominee — not even at the risk of electing Donald Trump.

Taken aback, Sanders and what remains of his campaign spent Monday trying to heal wounds that opened during the lengthy primary race and festered after the release of hacked emails from the Democratic National Committee.

Not even the slow-motion resignation of Rep. Debbie Wasserman Schultz (Fla.), the DNC’s embattled chairwoman, lightened the mood. In the streets, in the convention center where Sanders rallied and on the floor of the convention itself, some Sanders voters rejected the idea of ever backing Clinton for president.

“I fear Hillary more than I fear Trump,” said John Deebus, 66, who attended one of the many alternative events for democratic socialists and left-out activists in Philadelphia. “If Trump wins, he’s in for four years. If Hillary wins, she’s in there for eight. That’s not how we stop the corporate parties.”

Supporters of Bernie Sanders gathered outside City Hall in Philadelphia on Monday. Most vowed to never vote for Hillary Clinton, despite Sanders's encouragement to do so while speaking a few blocks away. (Alice Li,Jayne Orenstein/The Washington Post)

Sentiments like that had effervesced online for weeks. In Philadelphia, they were uttered within earshot of thousands of journalists and nearly as many cameras, amplifying each heckle and each peal of “Bernie or Bust!”

Sanders, who has repeatedly called for his movement to grow inside and not outside the Democratic Party, worked feverishly to change minds. After his speech to delegates, he dispatched deputy campaign manager Rich Pelletier to meet with Clinton aide Marlon Marshall. One result was an email message to all delegates and a shorter text message to the floor whips who were tasked with keeping delegations calm.

“Our credibility as a movement will be damaged by booing, turning of backs, walking out or other similar displays,” Sanders wrote in the email. “That’s what the corporate media wants. That’s what Donald Trump wants. But that’s not what will expand the progressive movement in this country. I know everyone is frustrated, especially by the recent DNC email disclosures. But, as a result of this disclosure Debbie Wasserman Schultz was forced to resign.”

At Sanders’s Monday event, the humiliating end of Wasserman Schultz’s DNC career was a huge applause line; it got the same reaction at a Sunday evening climate rally organized by Sanders delegates and Tom Steyer’s NextGen Climate.

But the perception that the primaries had been rigged — something that could not be undone by a firing — pervaded the mood of many Sanders delegates.

“Her resigning doesn’t change anything,” said Brandy Schappell, 33, who attended the climate rally. “It doesn’t do a damn thing to change the way that the primaries were rigged.”

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“It’s actually sort of an insult,” said Schappell’s husband, Ryan, also 33. “But it doesn’t make a difference to us. When Bernie endorsed Hillary, that was it — we re-registered with the Green Party.”

On Twitter, veterans of the Sanders campaign attempted to push back. “The contents of the leaked emails show individuals were definitely biased, but 7 folks on an email didn’t ‘steal’ the election,” wrote Symone Sanders, a former national press secretary for Bernie Sanders who is now assisting the DNC with the convention. “Other valid arguments, but a stolen election is not one. I worked there. No one stole the election from us.”

As TV networks played back the video of Sanders delegates booing Clinton’s name, Sanders deputy communications director Mike Casca tweeted a Pew poll, based on months of research, that found 88 percent of Sanders voters ready to back the ticket. “One more time with feeling, folks: The convention is not the election,” he wrote.

But some in Philadelphia wanted Sanders supporters to embrace the moment and quit the party. At one of two rallies Monday, the Green Party’s likely presidential candidate, Jill Stein, said the Democrats’ email hack revealed that the “worst fears and suspicions about the DNC” were true: First, Wasserman Schultz had limited Sanders’s opportunities to debate Clinton. Then, she and key staffers had taken every possible step to diminish him, Stein said.

“The fact that Hillary Clinton saw fit and the DNC saw fit to relegate Bernie Sanders to a footnote on the opening Monday evening instead of the night of the nomination is an outrage against this movement,” Stein said. “The future of this movement is not inside the Democratic Party.”

Plenty of Sanders’s delegates, and Sanders himself, disagreed — and were wrestling with how to prove it. The senator did not use his Monday afternoon speech to release his delegates, guaranteeing that Clinton will face a more robust vote of opposition than any Democratic nominee since the 1980s. It appears there will be no moment like the one in 2008, when Clinton personally interrupted the roll-call vote and asked for Barack Obama to be made the nominee by acclimation.

Sanders’s associates did little to capitalize on the unrest. As he prepared to step onto the blue carpet of the convention floor early Monday evening, Sanders campaign chairman Jeff Weaver swatted back the suggestion that the senator could revise his remarks in light of the nearly nonstop chants for him throughout the afternoon.

“No, no, no. We’re all about unity, my friend,” Weaver said. “It’s definitely a unity message.”

When asked about the chants of “Bernie!” and the cries against the Trans-Pacific Partnership trade pact, Weaver shrugged and said: “A lot of the party is anti-TPP. What’s the problem with that? The secretary is anti-TPP. What’s the problem?”

After the convention was gaveled in, both campaigns made bids for party unity. Supporters of both sides introduced a new “unity commission” that had come out of a compromise between Sanders and Clinton backers in the party’s rules committee — a panel empowered to cut the number of “superdelegates” unbound by the results of primaries.

“We did not win this by selling out,” said Diane Russell, a Maine legislator who led a campaign to end superdelegates in future primaries. “This is what democracy looks like.”

There were only scattered “no’s” when the commission was approved, but some Sanders-heavy delegations repeatedly booed at mentions of Clinton’s name, with some delegates standing and pointing their thumbs down. There were boos when prominent Sanders surrogates such as Rep. Raúl M. Grijalva (Ariz.) and former NAACP president Benjamin Jealous pointedly endorsed Clinton from the stage, and some quieter heckling when Clinton campaign chairman John Podesta attempted to pat Sanders delegates on the back.

“To everyone who supported Bernie Sanders: This is your victory, too,” Podesta said.

Before Sanders took the stage for his end-of-the-night speech, convention staffers handed out signs reading “I’m with her” and “She’s with us.” Then those signs were replaced with “Bernie” signs.

In his speech, Sanders endorsed Clinton even more strongly than he had at their unity rally in New Hampshire, reminding delegates that her defeat would mean a Supreme Court shaped by Trump.

“Hillary Clinton must become the next president of the United States,” Sanders said.

Robert Costa and Louisa Loveluck in Philadelphia, and John Wagner in Charlotte, contributed to this report.