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Bernie Sanders waved goodbye at the camera Tuesday night as he concluded an online discussion about the coronavirus. “Thank you very much, and we will see you all soon,” he said.

That casual farewell did not reflect the candidate’s intense deliberations off camera. By Wednesday morning, he would jump on a conference call with his staff to share words far more blunt: His five-year campaign to win the White House was over.

In a later video address, he explained the conclusion he was not able to escape in the weeks he had spent grappling about his political future.

“As I see the crisis gripping the nation,” a slightly hoarse Sanders told supporters in a live stream from his home in Burlington, Vt., “I cannot in good conscience continue to mount a campaign that cannot win and which would interfere with the important work required of all of us in this difficult hour.”

By midday, he had spoken privately to Joe Biden, now the presumptive Democratic nominee for president. Sanders in his video pledged to support the former vice president, although he said he will remain on primary ballots in an effort to collect enough delegates to influence the party’s platform in negotiations this summer.

In an interview on “The Late Show With Stephen Colbert,” Sanders praised Biden, but said he hoped to “move him in a more progressive direction.” Asked by Colbert if he was presenting a “full-throated endorsement,” Sanders replied that his team was in touch with Biden’s team to work on “how we can best go forward together.” Sanders added that although Biden holds different views, he “can indicate” to supporters of the senator that he is listening.

The departure of the senator from Vermont, a democratic socialist who rose from relative obscurity to build a movement and become a two-time runner-up for the nomination, marked the close of a roller-coaster primary race that started more than a year ago. What began as the most diverse presidential field in history, featuring more than two dozen candidates, finished as one white man in his 70s handed off the nomination to another. Biden’s own prospects had been written off not long ago, before a bracing and dramatic surge in the March primaries driven in part by the establishment closing in to embrace him.

Wednesday’s moves opened a new chapter that will test the Democratic Party’s ability to bridge lingering divisions between fervent liberal activists and more moderate party leaders that were evident in the wake of Sanders’s announcement. The immediate challenge: Can the party unify as it failed to do in 2016, when a feud between supporters of Sanders and Hillary Clinton damaged her efforts to win the presidency?

The decision also created uncertainty about the future of the Sanders movement, which is made up of legions of young, loyal supporters who packed rallies and stuffed his campaign coffers with record sums of cash. After his 2016 loss, many felt he would run again. Few believe that now, and some are contemplating who will lead them in the future.

One factor giving Democrats hope for healing is the expected reemergence of Barack Obama, who kept a low public profile during the primary. Obama had conversations with Sanders and Biden over the past few weeks focused on defeating President Trump, according to a person with knowledge of the talks who spoke on the condition of anonymity to discuss the private conversations. Obama is said to be determined to play a role in unifying and energizing the party for the general election.

Biden released a lengthy statement Wednesday lauding his rival’s accomplishments and saying that he would attempt to champion many of the same issues that animated his campaign.

“He hasn’t just run a political campaign; he’s created a movement,” Biden said, echoing a refrain from Sanders. “And make no mistake about it, I believe it’s a movement that is as powerful today as it was yesterday.”

But not everyone on Sanders’s side was ready to fall in line.

“While you are now the presumptive Democratic nominee, it is clear that you were unable to win the votes of the vast majority of voters under 45 years old during the primary,” said an open letter to Biden signed by eight liberal groups that encouraged him to adopt their ideas on climate change, health care and other topics. “Messaging around a ‘return to normalcy’ does not and has not earned the support and trust of voters from our generation.”

RoseAnn DeMoro, a close Sanders friend and former nurses union head, predicted Biden would have a “very, very heavy lift to get Bernie’s people on board” because, in her view, “he’s not inspirational.”

Some allies, however, were hopeful that a good personal rapport between the two men, who served together in the Senate, would help build cohesion among their backers.

“I believe a lot of progressives will rally around former vice president Biden as a bridge to a progressive future, understanding full well that if the Democrats do not unite to defeat Donald Trump and allow him to shape the courts and agencies for a generation, it hurts the progressive movement,” said Rep. Ro Khanna (D-Calif.), a national co-chair for Sanders.

Biden’s campaign expects to announce several policy agreements with Sanders starting Thursday, on topics including health care and student loans. “There’s work to do. We have to affirmatively reach out to them and let them know there’s home for them over here — and to court them,” said Rep. Cedric L. Richmond (D-La.), co-chairman of the Biden campaign.

Biden and his campaign for weeks have attempted to delicately pave the way for Sanders to exit the race, putting little public pressure on him while at the same time sending signals that they viewed the contest as all but over. Aides to the two men quietly conducted back-channel conversations.

Sanders on Wednesday congratulated Biden and called him a “very decent man, who I will work with to move our progressive ideas forward.”

Sanders’s decision to end his campaign closes one of the most remarkable chapters in modern political history. His advocacy for sweeping liberal ideas, such as Medicare-for-all and tuition-free public college, shifted the national debate over the role of government and found broad support among members of a party that he never formally joined.

“Together we have transformed American consciousness as to what kind of nation we can become,” Sanders said Wednesday. “Few would deny that over the course of the past five years, our movement has won the ideological struggle.”

His unexpected success in the first three primary contests of 2020, coming after he suffered a heart attack in October, made him the best-performing socialist contender in U.S. history, as well as the strongest Jewish presidential candidate. Sanders, 78, was also the oldest candidate to go so far in the process.

But his failure to capture the support of a majority of Democrats or win significant support in the African American community was on sharp display once the field narrowed to Sanders and Biden at the beginning of March, underlining the limits of his left-leaning politics.

He was never able to regain his footing and, as time went on, he faced internal pressure to think about stepping aside. In the run-up to Wednesday’s announcement, even some of his closest aides and allies had urged him to consider bowing out.

Yet he left the race having created a movement that could outlive his candidacy and be an influential force for years to come, given the passion of his supporters and their enthusiasm for his positions. “We have never been just a campaign,” Sanders said Wednesday, and his team promoted a new slogan, “The Campaign Ends, The Struggle Continues.”

Among some activists, Rep. Alexandria Ocasio-Cortez (D-N.Y.), a rising star who helped rescue Sanders’s candidacy with an endorsement after his heart attack, is seen as a potential successor. But some hard-liners are less sold on Ocasio-Cortez and view her as too conciliatory.

“Thank you for your leadership, mentorship, and example. We love you,” she tweeted of Sanders on Wednesday, along with a photo of them hugging.

The backdrop against which Sanders called it quits amounts to one more twist in a stretch of political history that has featured the most unorthodox president in memory, his impeachment due to an effort to politically wound a rival and investigations into Russian interference in U.S. elections.

Sanders vaulted onto the national scene in 2015 as a little-known challenger to Clinton, the overwhelming favorite for the Democratic presidential nod. While the senator from Vermont had spent decades in office, he had remained on the fringes of the political discourse, espousing ideas at the left end of the spectrum that often gained little traction.

He signaled his second candidacy with a bang, releasing a video in February 2019 that went viral and raising $6 million in his first 24 hours. That silenced critics who predicted he would struggle to generate excitement in a crowded field with a different dynamic than he faced four years before.

As fall arrived, Sanders struggled, falling behind as Biden and Sen. Elizabeth Warren (D-Mass.) ascended. His campaign screeched to a halt on Oct. 1, when Sanders was rushed to a Las Vegas hospital after suffering chest pains during a grass-roots fundraising event. Doctors later placed two stents to open a blocked artery, and it was not immediately clear whether Sanders would be able to continue his campaign.

Boosted back into contention by Ocasio-Cortez and other marquee endorsers, Sanders maintained a steady presence in the race as other candidates went up and down. His loyal backers gave him a floor of support. But as he later found, his polarizing politics also kept him from growing his base beyond a plurality of the party.

Sanders’s decision came after restrictions caused by the novel coronavirus halted all traditional forms of campaigning, denying him the giant rallies he had used to create a sense of momentum and cementing the former vice president’s growing advantage in delegates.

Biden’s campaign, like Sanders’s, has been separated as staffers and the former vice president have worked from their homes. Biden held several events online Wednesday in which he thanked Sanders and tried to raise money as the presumptive nominee.

“Thank goodness we can finally get to work,” Jill Biden told a group of donors, answering questions that included what focus she would have as first lady. “We could never presume that before. This has all been all brand new and happened so, so quickly.”

Chelsea Janes, Michael Scherer and Amy B Wang contributed to this report.