The Democratic presidential campaign took a dramatic turn on Sunday as a top candidate, former Mayor Pete Buttigieg,
Ratcheting up the pressure on Democrats to unite behind a single stop-Sanders candidate, an influential donor for Mr. Biden circulated an email to his political network calling for some rivals to the former vice president to drop out. At the same time, Bloomberg campaign officials presented internal polling projections to skittish Democratic Party leaders, arguing that Mr. Bloomberg’s presence in the race was actually containing Mr. Sanders’s potential to run up the score on Super Tuesday.
If Mr. Biden appeared suddenly ascendant on Sunday, the Super Tuesday map still favored Mr. Sanders, given his money, organization and breadth of support in key states. But the primaries on Tuesday remain highly volatile because so many Democrats are competing, each with some pockets of support in multiple states, and because Mr. Buttigieg’s departure make his supporters free agents.
Polls show Mr. Biden, Mr. Bloomberg and Ms. Warren are all at risk of falling short of the critical 15 percent threshold of support necessary to win delegates in various states and congressional districts on Tuesday.
Mr. Buttigieg, the first openly gay major presidential candidate, drew support from different ideological wings of the Democratic Party. With him out of the race, his backers could help one or more of those other candidates rise above the 15 percent margin. Some could also support Mr. Sanders.
Mr. Biden had been left for dead politically after three consecutive losses to open the contest, but he recovered on Saturday thanks to the strength of overwhelming support from black voters. He predicted their big vote of confidence would help reset a race that Mr. Sanders had been threatening to run away with.
The result was Mr. Biden’s best day of fund-raising since his launch — he raised $5 million on Saturday, and another $5 million on Sunday — as he reasserted the fundamental strengths of his candidacy.
“I think we’re moving into constituencies that when they hear me, they’ve always been mine. Diverse communities, white working-class folks, African-Americans and Hispanics, women in the suburbs,” Mr. Biden said on NBC’s “Meet the Press” on Sunday.
With the Super Tuesday primaries imminent, there were competing tactical imperatives on display on Sunday. Mr. Sanders — alone among the major candidates — skipped a commemoration of “Bloody Sunday” in Selma, Ala., flying instead to California for a pair of rallies in a state he leads in the polls and is worth nearly triple the delegates of all the February contests combined.
Mr. Biden, meanwhile, won the endorsement of Selma Mayor Darrio Melton and was received warmly at Brown Chapel A.M.E. church, as his speech was interrupted by a stream of affirmations as he denounced white supremacy. “Say it, Biden!” someone cried out.
Despite Mr. Biden’s decisive, nearly 30-point margin of victory in South Carolina, it was not clear how much his win would alter the hardening contours of the race. Millions of votes have already been cast in Super Tuesday states, particularly in California, and Mr. Biden has been dramatically outgunned on the airwaves and out-organized on the ground there. In February, Mr. Biden’s $18 million fund-raising total, announced on Sunday, amounted to less than 40 cents for every dollar that Mr. Sanders collected.
And in the last week, Mr. Biden essentially bunkered down in South Carolina to achieve his campaign-saving victory, while Mr. Sanders has been building up his operation, airing ads and making inroads across the country.
“They invested everything they had in South Carolina at the cost of everything else because they knew it was the only path forward,” Patti Solis Doyle, a Democratic strategist and former campaign manager for Hillary Clinton in 2008, said of the Biden operation. “It leaves them with incredible momentum, new energy but still lacking the resources and bodies to execute.”
What limited resources Mr. Biden has deployed in Super Tuesday states have been focused on buying ads on shows and stations that draw an outsized African-American viewership, according to a campaign official. His campaign previously announced a $2.2 million ad buy across eight states; the same Biden campaign official said they planned to use much of the new infusion of money to make investments in March 10 and March 17 states.
For now, Mr. Sanders has outspent Mr. Biden in Super Tuesday radio and television advertising by a margin of more than seven-to-one, according to the media-tracking firm Advertising Analytics; Mr. Bloomberg is outpacing Mr. Biden by closer to a 100-to-one margin.
Ari Rabin-Havt, a deputy campaign manager on the Sanders campaign, urged caution about over-interpreting the results from South Carolina and its impact. “Wait until you see what happens in other states,” he said. “I think taking one state and transmuting one state’s population to every state in the country is a mistake.”
Two other candidates in the race — Ms. Warren and Ms. Klobuchar — pressed to justify the rationales for their continued candidacies in memos, media appearances and appeals to the arcana of delegate math on Sunday, predicting a contest that would not be resolved until the convention this summer.
The Warren campaign memo about the post-Super Tuesday landscape was the most plain-spoken. “The reality of this race will be clear: no candidate will likely have a path to the majority of delegates needed to win an outright claim to the Democratic nomination,” wrote Roger Lau, Ms. Warren’s campaign manager.
The Warren campaign, he argued, was positioned to “ultimately prevail at the national convention in Milwaukee.”
An online gusher of donations has allowed those whose fund-raising might otherwise have dried up in past cycles to linger deeper into 2020.
Ms. Warren was on track to be the No. 2 fund-raiser in February, raising $29.3 million, despite never finishing better than third in any of the February contests. Ms. Klobuchar had hoped her surprise third-place finish in New Hampshire would propel her forward but while her momentum has long since evaporated, the money she raised provided a financial lifeline. She is now digging in to defend her home state of Minnesota on Tuesday.
Even Mr. Buttigieg had raised money steadily until the end, with an online counter on his website showing him more than $9 million toward his $13 million Super Tuesday goal when he dropped out.
It is not just Mr. Buttigieg’s supporters who are now up for grabs but the enviable network of big-dollar bundlers who helped him raise more than $82 million last year.
After his appearance in Selma, Mr. Biden headed to Virginia to rally supporters with two recent, big-name Democratic backers, Senator Tim Kaine, who had been Hillary Clinton’s vice-presidential pick four years ago, and former Gov. Terry McAuliffe, also a former chairman of the Democratic National Committee chairman.
The event was an establishment show-of-force that came after two other Virginia members of Congress, Representatives Bobby Scott and Jennifer Wexton, also endorsed him over the weekend, along with the former D.N.C. chairwoman, Representative Debbie Wasserman Schultz.
Mr. Bloomberg readied for his first test in Tuesday’s primaries after skipping the four early contests. He paid for a three-minute address to the nation on Sunday evening about the spreading coronavirus. Ms. Warren accused him of trying to “pretend he’s the president.”
Bloomberg advisers have grown frustrated with Ms. Warren’s repeated attacks, including in her commercials, and recently produced an ad hitting Ms. Warren for her reversal on super PACs, going from denouncing super PAC money to benefiting from the biggest super PAC ad buy in the race. Aides presented a plan to spend twice as much on the anti-Warren ad as Ms. Warren has spent on her anti-Bloomberg spots.
“Mike said no,” said Jason Schechter, a Bloomberg spokesman. “He wanted to stay positive.” (Mr. Bloomberg is running negative ads on Mr. Sanders but entirely online and not on television.)
For Mr. Biden’s supporters, the results in South Carolina and the departure of Mr. Buttigieg added fuel to their efforts to prune the field in hopes of setting up Mr. Biden as the single alternative to Mr. Sanders.
“The Democratic Party needs to come together behind Joe and make this a two person race,” Jon Henes, who was Senator Kamala Harris’s finance chair and now supports Mr. Biden, wrote to friends and other donors before Mr. Buttigieg quit the race, according to a person who reviewed the email.
He added, “Suspending a campaign is incredibly difficult for any candidate but right now we need our candidates to be realistic.”
A pro-Biden super PAC, Unite the Country, was even more direct, saying Mr. Bloomberg’s $500 million in advertising amounted to “the Bernie Sanders super PAC.”
“His entire argument for existence was Joe Biden stumbling — and after four states, Joe Biden has received more votes than anyone,” said the memo. “Mayor Bloomberg should decide soon if he wants to be the reason why Bernie Sanders is the nominee of the party.”
Shane Goldmacher reported from New York and Reid J. Epstein from Plains, Ga., and Selma, Ala. Reporting was contributed by Katie Glueck in Selma, Ala., Nick Corasaniti in Minneapolis and Sydney Ember in Norfolk, Va.