CONCORD, N.H. — The Democratic presidential race burst out of the New Hampshire primary this week into a new and highly unusual phase — with at least a half-dozen viable candidates, each facing an unpredictable path and major hurdles to overcome.

Typically, after the first two nominating contests, primaries narrow to a handful of front-runners as a campaign crystallizes between competing factions. This year, the race looks like no other Democratic primary in modern history, an increasingly muddled mix of ideologies, backgrounds and theories on what has unfolded.

Three contenders emerged from Tuesday’s vote here with added strength, with the top vote-getter a self-described democratic socialist and independent and the other two, both Democrats, vying to represent moderates. Two more candidates, including the party’s longtime national polling leader, leave the Granite State significantly weakened but vowing to fight on. And yet two more are self­-financing billionaires — one rising in South Carolina, which votes later this month, and the other gaining ground nationally and across Super Tuesday states.

None of the candidates has a clear advantage on the road to winning the 1,990 delegates needed to secure the nomination at this summer’s national convention in Milwaukee, and nearly all of them have struggled to appeal to crucial black and Hispanic voters as the campaign turns to more diverse states.

“There was no real winnowing process,” said Terry McAuliffe (D), a former governor of Virginia. “We’ve got seven candidates. We have seven candidates going forward, which is extraordinary.”

He added: “Now the real test for the candidates is: Can they build a coalition?”

Sen. Bernie Sanders (I-Vt.) has yet to show that he can attract a base broader than a quarter of the party’s voters — even in New Hampshire, where in victory he was unable to retain even half of the vote share he won four years ago.

Former South Bend, Ind., mayor Pete Buttigieg and Sen. Amy Klobuchar (D-Minn.) have enjoyed sudden spurts but have yet to demonstrate whether they can grow beyond their base of white voters.

Former vice president Joe Biden, who placed a dismal fifth, flew back to his home in Wilmington, Del., on Wednesday and held a call with donors to try to calm nerves and fill a depleted campaign account. The fourth-place finisher, Sen. Elizabeth Warren (D-Mass.), spoke via phone to rally her team late Tuesday, but also canceled television ads in Nevada and South Carolina starting next week.

Three candidates with less support dropped out of the race Tuesday night and Wednesday. But the Iowa and New Hampshire results have given more of the remaining candidates reason to stay in a race in which the unwieldy field has worked against any individual efforts to coalesce broader support.

In another sign of the turbulence engulfing the race, Troy Price, chairman of the Iowa Democratic Party, announced Wednesday he would step down, the latest fallout from last week’s botched Iowa caucuses, which resulted in delayed results and a chaotic outcome.

Looming over the South Carolina primary is billionaire Tom Steyer, who has spent freely to try to build support among black voters who previously were largely in Biden’s camp. Former New York mayor Mike Bloomberg’s deep-pocketed campaign will figure even more prominently when he begins appearing on ballots on March 3, Super Tuesday, when voting occurs in 14 states, including California and Texas.

So far, the way candidates have gained traction has been to attract a narrow slice of the electorate. Warren spent the past several weeks attempting to cast herself as a unity candidate and saw herself overtaken by Sanders, who made a forthright appeal to liberals, a more defined niche.

Adding to the muddle is the uncertainty evinced by voters. Half of New Hampshire’s Democratic voters said they decided whom to support in the last few days before the primary; about a third of Iowa’s Democratic voters said the same.

Democratic pollster Stan Greenberg said voters showed they were looking for a candidate who can beat Trump, and going forward, he said, the remaining candidates will have to make the case that they’re best positioned to defeat the president.

“I’m not sure many of these votes are very deep,” Greenberg said. “For me this is an anti-Trump Democratic primary electorate trying to find the best way to act on their hostility to Trump.”

Sanders on Wednesday didn’t appear to be attempting to expand his ideological reach. When asked if there are any lessons in the fact that he and Warren received fewer votes than moderates in the party, campaign co-chairwoman Nina Turner was blunt.

“The lesson to be learned,” she said on CNN, “is he won.”

Sanders already is tussling with the Culinary Union, the largest union in Nevada and one whose members, mostly Latino and female, typically play a major role in the caucuses. The union on Tuesday distributed fliers criticizing his Medicare-for-all plan, saying it would dilute the health-care plans that it has bargained for in negotiations.

The Sanders campaign countered with a statement noting he had joined unions on picket lines and saying his plan “is as comprehensive or more so than the health care benefits union workers currently receive.”

But later in the day, the union — which has yet to make a coveted endorsement — escalated the feud by releasing a statement criticizing his supporters, who it claimed had been critical of the union and its officials on Twitter and in phone calls.

“It’s disappointing that Senator Sanders’ supporters have viciously attacked the Culinary Union and working families in Nevada simply because our union has provided facts on what certain healthcare proposals might do to take away the system of care we have built over 8 decades,” the statement read. “We have always stood up for what we believe in and will continue to do so.”

Those in the party who are nervous about Sanders’s rise said Wednesday they took some comfort that voters are backing moderate candidates — but that was mixed with anxiety that Sanders could prove a durable force as he dominates on the left and those moderates divide up other voters.

“There is good news for people like us hoping a candidate other than Bernie emerges as a nominee,” said Matt Bennett, a co-founder and executive vice president at the centrist group Third Way. “But it’s going to be a real battle. The obvious problem for us is we have somewhere between three and four viable moderates. We don’t know whether either Pete or Amy can win outside of Iowa and New Hampshire. They don’t know that, either. Nobody knows that. They may get real momentum boosts in those places. They may not.”

He added: “We better get down to a smaller number of moderates pretty quick. Or else it’s going to make Sanders’s path, which is to ride a small plurality against a split field — that’ll make it possible. If we’re down to one-on-one, that won’t work.”

Buttigieg is doubling his Nevada staff, and his South Carolina team has swelled to 55 people. He announced the endorsement of J.A. Moore (D), a South Carolina state representative who had previously backed Sen. Kamala D. Harris (D-Calif.). Buttigieg also has the support of Walter Clyburn Reed, the grandson of South Carolina kingmaker Rep. James E. Clyburn (D), who has not endorsed a presidential candidate.

Klobuchar — who raised as much in the three hours after polls closed Tuesday as her monthly average last year — has rolled out a seven-figure ad buy in Nevada and plans to arrive in the state on Thursday.

Biden — joined by his wife, Jill, campaign manager Greg Schultz and senior adviser Anita Dunn — asked donors on a Wednesday afternoon call to be patient. They said the race was just beginning, noting a fact in which the campaign has been taking solace over the past few days: Bill Clinton won only one of the first 11 contests in 1992 before claiming the nomination.

Biden and campaign officials claimed that the campaign was “far from broke,” according to a person who was on the call, and suggested that Biden would undertake a brisker schedule through Super Tuesday. Officials also said that Bloomberg and Klobuchar were untested and would face far more scrutiny over the coming days.

Biden has several fundraisers scheduled for Thursday in New York, as well as one next week in Los Angeles co-hosted by Sen. Dianne Feinstein (D-Calif.). Those leading his super PAC are also trying to fill their account, with several meetings in New York on Thursday.

Biden’s campaign is hoping to regroup in Nevada, and amid a shake-up of its advisers has brought in a prominent Democratic consultant to help. Jen O’Malley Dillon, a top Obama campaign aide who ran the presidential campaign of former congressman Beto O’Rourke (D-Tex.) before he dropped out, is working on a volunteer basis.

But some Biden advisers say privately they are hoping for even a third-place finish in the state and that his organization is unlikely to match that of his rivals in the caucus state. Biden’s campaign leveled more pointed attacks against rivals Wednesday.

“We cannot afford to take a chance with a self-defined socialist, a mayor of a very small city, a billionaire who all of the sudden is a Democrat,” said Rep. Cedric L. Richmond (D-La.), co-chairman of the Biden campaign. “When people look at that in terms of what we have to lose and the risk of nominating somebody that’s not tested in that way, I think they will come back to Vice President Biden.”

His campaign also sought to focus on Bloomberg, whom it views as an increasing threat to Biden’s standing among black voters.

“Mayor Bloomberg is unvetted,” said Biden aide Symone Sanders. “Let me just say that again: Mayor Bloomberg is unvetted.”

Others outside the campaign suggested the pressure was on Biden.

“Joe Biden clearly has to show that there’s more there there after two defeats,” said Donna Brazile, a Democratic strategist and former interim chair of the Democratic National Committee.

Steve Westly, a top Biden fundraiser and former California state controller, said Iowa and New Hampshire demonstrated that the race in the moderate Democratic lane is still undecided.

“These are two tough losses for the vice president. Full stop here,” Westly said. “He’s going to have to turn it around. . . . Super Tuesday is going to be telling.”

Democrats expect the campaign to be litigated over weeks and maybe even months.

“This is going to be an absolute marathon of a primary season,” said Rep. Jamie B. Raskin (D-Md.), who is backing Warren. “We have a very choppy and divided picture.”

Michelle Ye Hee Lee and Chelsea Janes contributed to this report.