GREENVILLE, S.C. — Joe Biden did what he had to do, for the moment. And now, his supporters say, it is time for fellow moderates to do the same.
Mr. Biden made a compelling case on Saturday that he is the Democrat best positioned to head off the nomination of Bernie Sanders, the democratic socialist senator whom centrists fear would doom the party this fall. The former vice president did that by accomplishing something he had not managed across three presidential campaigns, spaced over more than three decades: He won a state.
Next comes the awkward part.
If a commanding victory in a place like South Carolina, built to reward Mr. Biden’s strength with black voters, helped mask some of his weaknesses for one week, his fate ahead of Super Tuesday is still shadowed by the preceding failures of both Mr. Biden’s campaign and the candidate himself. These aftereffects are already complicating a stretch that finds his rivals preaching patience as Biden allies demand urgency — and unity, around him.
After months as the front-runner, with the power to clear the field if he excelled, Mr. Biden is now a candidate at once determined and dependent. He is convinced that he has done enough to demonstrate his dominance with a core Democratic constituency but remains hamstrung on two fronts: by several competitors still disinclined to stand down, even if they siphon crucial non-Sanders votes, and by a campaign organization that party officials have described as jarringly thin in many of the states that will vote on Tuesday.
Mr. Biden’s ability to address either of these problems in time is far from assured, in a primary that has already exposed his capacity for bungling on the campaign trail, his enthusiasm deficit with many younger voters and his struggles in fund-raising.
Why would Michael R. Bloomberg step aside, before the states he is contesting have even voted, with hundreds of millions of dollars already sunk into his bid and a conviction that he is the man for the job?
What do Pete Buttigieg and Amy Klobuchar owe Mr. Biden, whom they each dusted in New Hampshire (and, in Mr. Buttigieg’s case, in Iowa), where the voters who spend the most time with their candidates decided that the former vice president could not be trusted to defeat President Trump?
The result, despite Mr. Biden’s undeniable success on Saturday, is a party establishment that agrees on the desired end of avoiding a Sanders nomination but is still bickering about the means.
The most creative among old-guard Democrats have spent recent weeks gaming out knotty scenarios to keep Mr. Sanders from the top of the ticket: a convention migration to another contender if Mr. Sanders falls short of a pledged delegate majority or the drafting, somehow, of a white-knight candidate who is not even running.
But settling for Mr. Biden would appear to be the straightest line. And in the coming days, his supporters plan to argue, loudly, that the time for dithering has passed.
“The case you’re going to make is, ‘Look, guys, this is the only alternative to Bernie, which is the only alternative to losing the election to Trump, and we need to consolidate,’” said Rufus Gifford, who was finance director for Barack Obama’s re-election campaign and supports Mr. Biden. But, he quickly acknowledged, “the big challenge there is Bloomberg. We all know that the Bloomberg vote is not going to Bernie, for the most part. So without a doubt, Bloomberg could be playing a spoiler.”
Top Democratic officials in key battleground states that go to the polls Tuesday, from Alabama to Texas, have said that Mr. Bloomberg poses an acute threat to Mr. Biden, eating into his standing with moderate voters. It does not help that early voting has already been underway in many states against the backdrop of Mr. Biden’s bleak finishes in Iowa and New Hampshire.
In interviews over the past week, a number of Mr. Biden’s top surrogates in key Super Tuesday states have heightened their attacks on the former New York City mayor, a sign of escalating tensions to come. “Bloomberg is spending a lot of money on the ground,” said Representative Terri Sewell, Democrat of Alabama. “But there’s one thing I know for a fact: People in my district died and fought for the right to vote, and that vote is not for sale.”
Yet the Alabama Democratic Conference, a powerful black caucus in the state, has endorsed Mr. Bloomberg, as has Anthony Daniels, the state House minority leader.
In North Carolina, too, Mr. Bloomberg has racked up a host of powerful endorsers and locked down some of the state’s top strategists. Representative Alma Adams, a Biden supporter, was sharply dismissive, calling Mr. Bloomberg “doomed” in the state and noting that he was once a Republican.
“People aren’t stupid around here,” she said. “I think he’s trying to trick his way in, claiming to be a Democrat and claiming to have close ties with Obama.”
Mr. Bloomberg’s presence is not the Biden campaign’s only cause for concern. On Saturday, Mr. Biden’s most important endorser in South Carolina, Representative James E. Clyburn, acknowledged organizational problems and, in a CNN interview, raised the prospect of assessing “how we retool this campaign.”
But Biden advisers are hoping that his victory in South Carolina will resonate in states, congressional districts and media markets that, like this state, have a significant base of African-American Democrats.
Mr. Biden is scheduled to visit Selma, Ala., and Norfolk, Va., on Sunday, and Houston and Dallas on Monday before heading to California. The campaign is also optimistic about an influx of cash that traditionally comes with primary victories. Such an infusion could be plowed into both his Super Tuesday operation and the states that vote later in March. There are also efforts underway to organize fund-raisers throughout the rest of the month.
“Hopefully, some other of the candidates will really start thinking about, you know, stepping away and letting this race shape up where the democratic socialist folks can have their say, and the moderates to the left can have their say,” said Representative Tim Ryan, Democrat of Ohio and a former 2020 presidential candidate who is supporting Mr. Biden. “And we can have an argument to the finish.”
Mr. Ryan said that he would be at one of several organizing events the campaign is holding in his state on Sunday. He hopes to convince Sanders opponents that Mr. Biden must be embraced for the good of the party.
Of course, “the party” is less a monolith than an unruly collection of fiefdoms, none necessarily powerful enough to make candidates or voters come to heel through sheer force of will or strongly-worded-statement.
For 2020 contenders, who have committed a year or more to the cause, the incentives to drop out have perhaps never been weaker than in this political era. Even lower-polling candidates are often still drawing large crowds, still appraising a field without a runaway favorite, still being told that the fight is worth fighting, especially in a campaign so unpredictable.
“Everybody believes they are two days away from the big turnaround,” said Jennifer Palmieri, a former top aide to Mr. Obama and Hillary Clinton. “It’s also a candidate and staff on the ride of their lives. To be like, ‘We’re going to drop out and go back to the Senate on Tuesday’ — it’s just not appealing.”
Some Democratic eminences have begun hinting unsubtly, after an early primary season in which an unusually large number of credible choices have stayed on the stage.
Barbara Boxer, a former California senator who spoke fondly of Mr. Biden, her onetime colleague, said she would “never tell other people what to do.” But underperforming candidates, she added, “ought to look at what their staying in the race means to the country, to the party and to their own reputations.” Ms. Boxer said she hoped to announce an endorsement on Sunday.
Many Biden-inclined voters have been less diplomatic. After the former vice president’s event in Spartanburg, S.C., on Friday evening, Antwion Yowe, 43, a local pastor, summoned a favored family analogy about separating standout options from the rest.
“My dad used to say: ‘barbecue and mildew,’” he said. “You’re either barbecue and you go forward, or you’re mildew and you’re done.” After South Carolina, he suggested, everyone except Mr. Biden and Mr. Sanders belonged in the latter camp.
Even if his peers were to fall away, Mr. Biden’s path would not be straightforward. Mr. Sanders has shown himself capable of building a formidable coalition, particularly in his blowout win in Nevada a week ago. He remains the favorite in California, the grandest delegate trove on the map. He has also flashed a victor’s swagger in scheduling events in the home states of two fellow hopefuls, which also happen to have primaries on Tuesday: Massachusetts, represented in the Senate by Elizabeth Warren, and Minnesota, the province of Ms. Klobuchar.
Any further setback for Ms. Warren could prove especially helpful to Mr. Sanders, potentially sending some of her progressive supporters into his camp. But voters do not always behave ideologically, a fact that cuts both ways for Mr. Sanders as Mr. Biden banks on a boost if other center-left candidates drop out: Some of that support will drift to Mr. Sanders even if voters do not align precisely with him on policy.
For one evening, though, Mr. Biden and his team seemed content not to dwell much on any of that. He had waited more than 30 years to win a presidential primary contest.
He had three whole days before he would have to do some winning again.