Former vice president Joe Biden moved aggressively Sunday to capi­tal­ize on his dramatic South Carolina victory, welcoming a round of key endorsements and insisting in television interviews that he alone can unite his anxious party and stave off the ascent of Sen. Bernie Sanders (I-Vt.).

Biden’s newfound confidence came as like-minded contenders confronted pleas to drop out and back him ahead of this week’s primary elections — and as Democratic operatives deliberated over the timing and nature of those decisions.

A significant boost for Biden came Sunday evening, when former South Bend, Ind., mayor Pete Buttigieg — one of his rivals for moderate votes — ended his campaign with a speech that, while not an endorsement, echoed Biden’s arguments for consolidating behind him.

Several influential Democrats from Super Tuesday states also gave Biden a lift on Sunday as they announced their support, including former senator Barbara Boxer of California. In Virginia, Rep. Jennifer Wexton — who won her suburban district in 2018, turning the seat blue for the first time in 38 years — endorsed Biden, calling him a “steady, empathetic leader.”

Wexton’s nod came after other prominent Virginia Democrats such as Sen. Tim Kaine, former governor Terry McAuliffe and Rep. Robert C. “Bobby” Scott endorsed Biden — a reflection of the urgency in the party’s establishment to counter the rise of Sanders, a self-described democratic socialist.

Biden’s efforts are rooted in his campaign’s belief that he needs to use the burst of momentum and attention from South Carolina to rally Democrats to his side before Tuesday’s elections, when 14 states and one territory will vote to award 34 percent of the convention delegates. Biden has lagged behind rivals in organizing and fundraising for months.

Biden attempted to make up for past deficiencies with a round-robin set of television appearances in which he contrasted his centrist approach with Sanders’s pitch for a federal overhaul, which centers on a move toward a single-payer health-care system.

“People aren’t looking for a revolution,” Biden said on CNN’s “State of the Union.” “They’re looking for results.”

On NBC’s “Meet the Press,” the former vice president boasted of the gains already seen by his campaign, which has struggled since its start to keep pace with better-financed candidates.

“A lot of supporters stepped up the last 24 hours; we raised over $5 million,” Biden said.

While Saturday’s South Carolina’s primary was a thunderclap — Biden decisively won the contest, in which African American voters had a significant say for the first time this election season — it provided a crucial affirmation of his candidacy rather than a guarantee of coming success. Sanders is polling strongly in many Super Tuesday battlegrounds, and former New York mayor Mike Bloomberg has spent hundreds of millions of dollars on advertising in those states.

Sens. Elizabeth Warren (Mass.) and Amy Klobuchar (Minn.) and Rep. Tulsi Gabbard of Hawaii remained in the Democratic race on Sunday night. But throughout the day, there was pressure on Buttigieg and Klobuchar, in particular, to consider ending their bids after they struggled in South Carolina and the Nevada caucuses to expand their appeal among minority voters. Liberal investor Tom Steyer dropped out of the contest late Saturday.

Those conversations — a flurry of phone calls and meetings — rippled with political calculations as top Democrats mapped out the brutal stretch ahead.

For many Biden allies, Bloomberg — the billionaire centrist whose name will appear on ballots for the first time Tuesday — remains the biggest headache, and they are hopeful that he may soon decide to bow out. On Sunday, they passed around a clip from MSNBC in which David Plouffe, Barack Obama’s 2008 campaign manager, said, “The reality is Bloomberg needed Biden to lose South Carolina to have any chance.”

“Bloomberg is the one in focus because he has the resources to go on indefinitely and compete and divide the center-left vote with Biden,” said David Axelrod, a senior adviser in the Obama White House.

Although Biden’s campaign would welcome a narrowed field, several allies are also informally telling allies of Klobuchar and Warren to consider staying in the race until Tuesday night, to deny Sanders a major delegate haul in the Super Tuesday states of Minnesota and Massachusetts, according to three people briefed on the talks who spoke on the condition of anonymity to speak frankly.

In the arcane process that Democrats use to pick nominees, delegates are awarded proportionally to any candidate who hits a threshold of 15 percent of the vote. Those rules put a premium on candidates who have broad support to win statewide, which determines a portion of the delegates, and also win individual congressional or state Senate districts, which account for the rest. And the setup benefits campaigns that can pinpoint the areas where they can either win a few extra delegates — or potentially deny an opponent from doing so.

Fourteen states and one U.S. territory will hold nominating contests on Tuesday, to award about one-third of the 1,991 delegates needed to clinch the nomination. Tuesday’s states also include Arkansas, Maine, Utah, Oklahoma and Colorado.

After winning 60 percent of the African American vote in South Carolina, Biden’s Super Tuesday outlook is best in states where those voters represent a high percentage of the Democratic electorate, such as Alabama.

“Once things start settling, you’ll see that Joe Biden will overwhelmingly take more delegates,” Frank Love, the Arkansas state House minority leader, predicted Sunday, as Biden’s wife, Jill, campaigned in North Little Rock. The core reason, he added, was that Biden was the partner of “the greatest president of our generation” and is ready to defeat Trump and pick up that Obama legacy.

Sanders’s campaign aides say that he is ready to make gains with younger, more liberal African American voters in states such as North Carolina and have argued that South Carolina is older and more moderate than most of the states voting on Tuesday.

“Wait until you see what happens in other states,” said Sanders deputy campaign manager Ari Rabin-Havt. “Transmuting a population, one state’s population to every state in the country, is a mistake.”

Bloomberg has attempted to make inroads with African American voters but has encountered continued problems over his past support of stop-and-frisk, a police strategy that opponents say is a form of racial profiling. Before announcing his candidacy, he apologized for defending the practice.

As Bloomberg spoke Sunday in Selma, Ala., at Brown Chapel AME Church, about 10 people stood and silently turned their backs to him. They returned to their seats after the former mayor stepped away from the podium. The incident caused a stir in the church, but Bloomberg continued his remarks without interruption. Other attendees continued to listen, some cheering and applauding.

Biden and Sanders are now running near polar opposite campaigns. The once-ailing Biden operation is trying to ride the wave of momentum and attention as he reminds voters of his work alongside Obama and warns them of the perils of backing Sanders.

“I have gotten major, major things done. I’m able to cross the aisle and get things done. And so I think it’s about who can not only win, bring along a Senate and keep a House, the House of Representatives, but who can then get something done,” Biden said on CNN.

He said on ABC’s “This Week” that, while it would be difficult, he could “make up a lot of ground in California” by Tuesday. “Super Tuesday is not the end; it’s only the beginning,” he said.

Sanders, meanwhile, is roaring before thousands at rallies and is counting on his grass-roots organizing in states such as California and Texas, which he has been building since his insurgent 2016 campaign.

Sanders raised $46.5 million in February, his presidential campaign said Sunday, a huge sum that could help sustain him in a lengthy battle for the nomination. The senator from Vermont won nominating contests in Nevada and New Hampshire last month before placing a distant second in South Carolina.

Sanders, who has sharply criticized Biden for his past backing of military intervention in Iraq and his support of free trade, attacked Biden on Sunday as an ally of the wealthy and centrist Democratic establishment that he is trying to overhaul.

Speaking at a rally in San Jose on Sunday, Sanders said: “At a time when the American people are sick and tired of endless wars, of the terrible death rate we have seen from these wars, the trillions of dollars we have spent on these wars, please do not forget Joe Biden voted for the war in Iraq.”

“We’ve got to be honest,” Sanders told the crowd. “Which campaign can beat Trump?” His supporters chanted “Bernie! Bernie!”

Most national Democrats treaded carefully as they approached the candidates and senior aides to struggling campaigns, knowing that the decision to drop out is deeply personal as well as political. With Obama on the sidelines and former nominee Hillary Clinton also quiet, there was also open debate about who, if anyone, had enough political capital to force an exit.

Former Democratic National Committee chairman Howard Dean, recalling his past presidential campaign, said the process can be painful for candidates who “feel they owe it to their supporters, many of whom put their whole lives on hold, to carry on.”

And in interviews with more than a dozen operatives, lawmakers and campaign aides, who requested anonymity to speak frankly, it was clear that House Speaker Nancy Pelosi (D-Calif.) and Obama, among others, are reluctant to do anything at this point that would seem heavy-handed.

Biden, in the ABC interview, dismissed the notion that Obama’s lack of endorsement leaves him vulnerable.

“No, it isn’t hurting me, and I don’t think it’s time,” Biden said. “He and I have talked about this in the very beginning. I have to earn this on my own.”

Warren, for her part, showed no signs of relenting. Her campaign announced that she raised $29.3 million last month, more than doubling her January haul thanks to a boost from her well-reviewed debate turn in Nevada — and the campaign increased its advertising spending in Super Tuesday states to $2.4 million. A pro-Warren super PAC is also spending millions.

Klobuchar’s aides and confidants said she was campaigning hard ahead of Super Tuesday and felt good about her chances in her home state.

“I want to go everywhere,” Klobuchar told a Utah television station on Sunday.

Buttigieg on Sunday met with former president Jimmy Carter near Carter’s home in Plains, Ga. Carter, who has been friendly with the 38-year-old Democrat, told reporters, “He doesn’t know what he’s going to do after South Carolina.”

Buttigieg replied, “Every day, we’ll do the math.”

Hours later, Buttigieg dropped out before a rapturous crowd in South Bend that chanted “2024! 2024!”

“The truth is that the path has narrowed to a close for our candidacy, if not for our cause,” he said.

Sean Sullivan, Cleve Wootson, Dave Weigel, Isaac Stanley-Becker and Matt Viser contributed to this report.