It did not take much for Joe Biden to distinguish himself from his main rival for the Democratic nomination.
“If the Democrats want a nominee who’s a Democrat, a lifelong Democrat, a proud Democrat, an Obama-Biden Democrat,” he thundered triumphantly after his momentum-turning victory in South Carolina in February, “then join us!”
Bernie Sanders is not a lifelong Democrat. He is not an Obama-Biden Democrat. He is not even a Democrat.
But that is not stopping the party from trying to make him feel welcome — now that it has stopped him from being its leader.
When Mr. Sanders dropped out of the presidential race a week ago, a Democratic establishment that has long kept him at arm’s length raced to publicly embrace him. Since he endorsed Mr. Biden, the former vice president, on Monday, party leaders have lavished Mr. Sanders with praise.
“Bernie is an American original, a man who has devoted his life to giving voice to working people’s hopes, dreams and frustrations,” former President Barack Obama said plainly in a video on Tuesday that announced his support for Mr. Biden. Never mind that Mr. Biden had spent part of the Democratic primary race accusing Mr. Sanders of disloyalty for considering a primary challenge against Mr. Obama in 2012.
A day earlier, Mr. Biden had called Mr. Sanders the “most powerful voice for a fair and more just America,” then theatrically acquiesced to Mr. Sanders’s quip that they play chess. A former top aide to Hillary Clinton enthused that Mr. Sanders was selfless.
This rush to show appreciation for Mr. Sanders, an independent senator from Vermont who has spent much of his political career railing against the Democratic establishment, is partly an exhalation of relief.
In 2016, Mr. Sanders stayed in an increasingly bitter primary race even after it became clear that Hillary Clinton would be the nominee. Some of his supporters, viewing the race as rigged, pledged their allegiance to him and vowed never to support Mrs. Clinton. Some voted for President Trump. With Mr. Sanders’s recent unity-building activities, fears that he would inspire the sort of divisiveness that many in the party still blame for the election of Mr. Trump have been momentarily assuaged.
It is also a recognition that Mr. Sanders has moved the party to the left, introducing policies like “Medicare for all” and tuition-free public college that are now embroidered into the fabric of the party.
But perhaps above all, it is a projection of how desperate Democrats are to beat Mr. Trump. Establishment Democrats recognize that if Mr. Biden is to win in November, he will need the backing of Mr. Sanders’s loyal supporters, some of whom have expressed reluctance, if not disgust, at the notion of voting for the former vice president. By showing Mr. Sanders gratitude, they are hoping to mollify his supporters, too.
On Wednesday, Mr. Sanders’s campaign manager, Faiz Shakir, was circumspect about the establishment’s newfound respect for his boss.
“He’s a person who has unrivaled integrity among many politicians,” he said. “When the dust settles, people recognize that integrity.”
Mr. Sanders, who is 78, said this week in an interview with The Associated Press that it was “probably a very fair assumption” that this presidential campaign was his last. But Mr. Shakir rejected the idea that Mr. Sanders was guided by a wish to cement a positive political legacy in the eyes of a party he has long loathed.
“That’s not the way he thinks,” he said. “He does not think on legacy terms.”
For months, Mr. Sanders had said he would do everything he could to support the eventual Democratic nominee. “I hope it’s me,” he would say, before quickly committing to work with whomever it was to defeat Mr. Trump.
The establishment’s Sanders adoration is also reflective of a rite of passage for past presidential hopefuls, and Mr. Sanders is joining a long line of losing candidates who seemed more palatable to onetime critics in hindsight. As the presumptive nominee is prodded for flaws, the flaws of former rivals melt away.
The former Vice President Al Gore, caricatured as boring and stilted when he ran for president in 2000, became revered by Democrats as a visionary who might have been able to save the country from former President George W. Bush. Democrats also looked fondly back at Senators John McCain, of Arizona, and Mitt Romney, of Utah, as pre-Trump Republicans who were actually never that bad. Mrs. Clinton was especially popular among Democrats after she lost to Mr. Obama in 2008.
Now Mr. Sanders is in the uniquely awkward position of being venerated by a party he has never joined but which he has shaped so much that it now can’t push him away.
The result is an exaggerated alliance that is aimed at soothing intraparty tension — with the added effect of calling into question whether political messages are simply a form of competitive posturing: For the moment, at least, voters can have an Obama-Biden-Sanders Democrat, a new political category that suggests identifying with the party means having everything or nothing at all.
During the campaign, one of Mr. Biden’s sharpest attack lines against Mr. Sanders came in Iowa in late January when he accused his rival of not being a member of the party.
“I’m a Democrat,” Mr. Biden said, discussing contrasts with his rivals, as if to dismiss Mr. Sanders completely. His diatribe provoked a biting response from Mr. Shakir, who replied, “Last-minute cheap barbs of desperation aren’t a good look for a candidate who proclaims his desire to unite the party.”
Now, of course, the candidate who made that barb has united the party enough to earn the endorsements of both Mr. Sanders and Senator Elizabeth Warren of Massachusetts, whom he had cast as elitist with a “‘my way or the highway’ approach to politics.”
On the other end of the Democratic spectrum, Mr. Sanders’s protégé, Representative Alexandria Ocasio-Cortez of New York, has similarly distanced her brand of politics from Mr. Biden’s.
“In any other country, Joe Biden and I would not be in the same party, but in America, we are,” she said in a January article in New York Magazine.
Now Mr. Biden, Mr. Sanders and Ms. Warren are united, and Ms. Ocasio-Cortez has suggested she may join them. In an interview with Politico on Wednesday, she stopped short of endorsing Mr. Biden but suggested she might do so soon.
“When you disagree, he’ll listen,” Ms. Warren said about Mr. Biden on Wednesday in her endorsement video. “Not just listen, but really hear you and treat you with respect, no matter where you’re coming from.”
And in a potential sign of the Sanders campaign’s willingness to let bygones be bygones, Mr. Shakir said on Wednesday that the January episode with Mr. Biden “didn’t leave any indelible impression.”
He also challenged the meaning of being a Democrat in the first place.
“There’s long been kind of a tension of whether a Democrat is defined by the partisan ‘D’ next to their name,” he said. “What Bernie has always pushed this party to reconcile is we stand for something and that’s what brings us together — it’s not a label.”
Some of Mr. Sanders’s devoted backers, including his former national press secretary, have indicated they have no such plans to fall in line. They have made clear that Mr. Sanders does not speak for them even as he has urged them to back Mr. Biden as well.
But for many Democrats, the overwhelming longing to beat Mr. Trump is enough to erase any lingering acrimony and bridge the ideological gulf.
After Mr. Sanders endorsed Mr. Biden, Tom Perez, the Democratic National Committee chairman, retweeted Mr. Sanders’s announcement, writing: “Unity is our greatest strength and Donald Trump’s worst nightmare. I’m proud to spend the next 204 days in this fight together.”
Even some former staff members for other presidential campaigns were eager to jump in.
“Bernie living his campaign’s mantra today of #NotMeUs & I respect the hell out of it,” Lily Adams, the communications director for Senator Kamala Harris’s campaign, tweeted on Monday. “Great news moving into the next phase of the election.”
In an interview, Ms. Adams, who was also a spokeswoman for the 2016 Clinton campaign, said that she admired Mr. Sanders for putting the Democratic Party and the country ahead of his own run.
Candidates like Mr. Sanders who are willing to sacrifice their ideals in the interest of beating Mr. Trump, she said, “will and should get praised.”