Manchester, New Hampshire CNN  — 

Joe Biden is flying to South Carolina on Tuesday night, bailing at the last minute on his planned New Hampshire primary-night party ahead of another expected loss.

The former vice president’s abrupt change of plans comes as his campaign scrambles to keep his base of African-American support from crumbling under the weight of a fourth-place finish in Iowa and another potentially poor showing here.

Biden told reporters Tuesday in New Hampshire he’s leaving because there are “significant portions of the electorate who haven’t voted yet.”

“We’re still mildly hopeful here in New Hampshire,” he said. “And we’ll see what happens.”

Biden’s campaign and his allies are urgently attempting to convince Democrats not to write the former vice president off until states with more of the African-American and Latino voters who are crucial to the party’s base have had a chance to cast ballots.

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“The problem with the primary schedule is that you can build a momentum and have absolutely no diversity of support,” said Louisiana Rep. Cedric Richmond, Biden’s campaign co-chair. “And so, we just have to remind people that the two states that are diverse speak next and that will change the tide of momentum.”

North Carolina Rep. Alma Adams, a Biden supporter whose state votes on Super Tuesday, said Iowa and New Hampshire are “not reflective of what I know will be strong support” for the former vice president in more diverse states.

“It doesn’t look like our communities across the country. It doesn’t look like the party at all,” she said of the nominating contest so far.

Already, though, Biden’s campaign was showing signs of deep concern that his fourth-place finish in Iowa and anticipated loss in New Hampshire would damage his standing elsewhere.

Biden held a phone call with top South Carolina supporters on Monday that was led by senior adviser Symone Sanders. His campaign had already announced it was dispatching Richmond to a party Tuesday night – originally scheduled to take place 30 minutes after the polls closed in New Hampshire.

In addition to Vermont Sen. Bernie Sanders and former South Bend, Indiana, Mayor Pete Buttigieg, the top two finishers in Iowa, aides and allies are also increasingly focused on a rising new threat: former New York City Mayor Mike Bloomberg.

A Quinnipiac University poll released Monday showed that Biden remains the leader among black Democratic primary voters nationally – but that his lead had shrunk from 49% in late January down to 27% just two weeks later.

And for the first time, others were right on his heels among black voters: Sanders was up to 19%. And Bloomberg – fueled by hundreds of millions of dollars in advertising in Super Tuesday states and beyond – had jumped to 22%.

Biden didn’t seem to know about the poll hours after it was released.

“I think it’s an outlier,” he said when CNN’s Don Lemon asked about it.

Asked on MSNBC on Tuesday morning about Bloomberg’s rising support among black voters, Biden said: “It’s amazing what $500 million can do in terms of being on the air.”

Already, Biden’s allies are casting doubt on whether Bloomberg could turn in the kind of performance with black voters in a general election that Democrats need to defeat President Donald Trump.

The treasurer of a pro-Biden super PAC, Larry Rasky, is warning donors of a “doomsday scenario” if Biden is not the nominee.

“Joe Biden is the first front runner never to be fully resourced. You can change that and it needs to happen soon. Bernie could come rolling out of New Hampshire with too much steam to be stopped by anyone but Joe. And Mike offers a faulty safety valve,” Rasky wrote in a memo obtained by CNN.

Richmond said Trump’s State of the Union speech offered a preview of how he’d attack Bloomberg in a bid to convince African-Americans not to vote in November.

“He’s going to go out and talk about the fact that Bloomberg did not support President Obama, that Bloomberg had stop and frisk, that Bloomberg was a Republican,” Richmond said. “And he’s going to do all of that to just try to take 8, 9% of the African-American vote or get people to stay home.”

CNN’s Arlette Saenz and Jessica Dean contributed to this report.