MANCHESTER, N.H. – Joe Biden is heading south.

The former vice president abruptly announced on Tuesday morning that he won’t spend primary night in New Hampshire as planned and instead is flying to South Carolina to headline a newly scheduled kick-off rally in the state he’s long considered his campaign firewall.

“We’re going to head to South Carolina tonight,” Biden told reporters as he visited a polling station with voting underway in the state that holds the first primary in the race for the White House. “And I’m going to Nevada… we’ve got to look at them all.”

The campaign confirmed Biden is now canceling his originally scheduled appearance at a primary night party in Nashua, N.H., and will be in South Carolina instead. The New Hampshire party will go on as scheduled without him. But the campaign emphasized that Biden would continue to stop by polling stations during the afternoon.

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Nevada and South Carolina follow New Hampshire – which is an overwhelmingly white state – in the presidential nominating calendar. Biden’s campaign has long considered Nevada and South Carolina – with their far more diverse electorates – as much friendlier ground for the former vice president.

Biden, who limped into New Hampshire after a lackluster fourth-place finish in last week’s Iowa caucuses, said Monday night to his supporters: “Stick with me 24 hours and we’re going to be just fine. We’re going to win this nomination.”

On Tuesday he said he was still “mildly hopeful” about his prospects in New Hampshire, while also downplaying expectations consistently for the Granite State.

“I took a hit in Iowa and I’m probably going to take a hit here,” Biden said in a striking moment at the top of Friday night’s Democratic presidential nomination debate.

Asked the next day by Fox News if he was writing off the Granite State, the former vice president fired back, saying “I’m not writing off New Hampshire. I’m going to campaign like hell here in New Hampshire, as I’m going to do in Nevada, in South Carolina and beyond. Look, this is just getting going here. This is a marathon.”

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For Biden, however, at least a third-place finish here could be critical, if only to prevent an exodus of donors and the possible erosion of his so-called "firewall" of support in the looming South Carolina contest. With the race for first increasingly looking to be between Sen. Bernie Sanders and Pete Buttigieg, Biden’s essentially battling with Sen. Elizabeth Warren and Sen. Amy Klobuchar of Minnesota for a top-three ticket out of the Granite State.

It's a stunning predicament for the candidate who was once the unrivaled front-runner for the nomination. He's long made electability central to his campaign pitch. But University of New Hampshire pollster Andrew Smith highlighted that the final UNH tracking poll for CNN, conducted after Biden’s fourth-place finish in the Iowa caucuses, indicated that “Bernie Sanders is seen as the most electable candidate” to take on Republican President Donald Trump in November’s general election.

“If your candidacy is based on electability, once you don’t win elections, that electability argument dissipates very rapidly,” Smith explained. “If Biden does very poorly in New Hampshire, going forward those voters in Nevada and South Carolina are going to look at that electability argument in a very different light because to be electable, you need to win elections.”

Democratic nomination rival Sen. Bernie Sanders of Vermont – asked whether Biden’s departure to South Carolina before the polls says something about the former vice president’s prospects in New Hampshire – answered, “You have to ask Joe. I don’t know.”

But Sanders stressed: “All I can say is we’ll be here tonight. We have, as you know, been all over the state.”

Longtime state Sen. Lou D’Allesandro – a top Biden supporter and surrogate in New Hampshire – told Fox News that “some supporters would be discouraged, obviously. But the positive aspect is it’s on to Columbia, it’s on to the next challenge, and then it’s on to Nevada, another challenge, and the game keeps going on.”

D’Allesandro – who met with Biden Tuesday morning at a polling station in Manchester – shared that “I feel a little badly that he’s not going to be here, but I’m with him. I’m going to stay with him. It’s on to Columbia and we’ll win in South Carolina.

Meanwhile, the pro-Biden super PAC ‘Unite the Country’ – in a memo sent out to donors to “dig deep right now” into their pockets – warned that “donors hedging their bets on Biden because of (Mike) Bloomberg could be creating a doomsday scenario for the Democrats everywhere.”

The memo, obtained by Fox News, is a sign of deep concerns among Biden supporters. It argued that the “Sanders-Warren wing of the Party is ready for the Bloomberg fight. Democrats cannot afford a split Convention.”

And the memo predicted that if "Bernie has more delegates, do you really think the Bros will make way for Mike?"

The ‘Bros’ refers to hard-core Sanders supporters.

"Not to mention that the legacy of the Sanders campaign (such as the Squad) will ravage any chance Center-Left Democrats have of maintaining hard won victories in states from Pennsylvania to California,” the memo added.

Fox News' Andrew Craft contributed to this report.