• Nikki Haley is facing pressure from some of her top fundraisers to either seriously compete with, or outright defeat, Donald Trump in New Hampshire.
• "I would still like to see her get somewhere but the mountain she has to climb is enormous," said Andy Sabin, a New York businessman and Haley fundraiser. "I don't even know what Trump could do to stop himself right now."
• If Haley falls short, some donors may try to find other ways to stop Trump, including possibly by financing a third-party effort like No Labels, said a Republican fundraising advisor.

Former United Nations ambassador Nikki Haley is facing pressure from some of her top fundraisers to either seriously compete with, or outright defeat, Donald Trump in next week's New Hampshire primary, after finishing third on Monday in the Iowa caucus.

"I would still like to see her get somewhere, but the mountain she has to climb is enormous," Andy Sabin, a New York businessman and Haley fundraiser, told CNBC. "As much as I like Haley, I don't even know what Trump could do to stop himself right now."

Sabin plans to help raise money for Trump if Haley doesn't make it through the primary season, despite previously telling CNBC he wouldn't give the former president "a f---ing nickel."

"He may be the only choice I have," said Sabin.

Several Haley fundraisers who spoke to CNBC conceded that, unless she gets a very close second to Trump or manages to pull off an upset win in New Hampshire, the race could effectively be over for her after that.

New Hampshire "is critical. If she wins there, and she can, it will be a long primary season," said Eric Levine, an attorney and bundler for Haley.

Levine is also the co-host of a Haley fundraising event scheduled for after the New Hampshire primary. He told CNBC he isn't worried about poor attendance, as long as she has a strong showing in the Granite State.

"She needs to win or a very, very close second place," said a lobbyist who is raising money for Haley.

To keep many of her more affluent donors engaged, Haley must get within three percentage points of Trump in New Hampshire, said a Republican fundraising advisor whose clients include Haley donors. If she does not, these donors could turn away from Haley and try to find other ways to stop Trump, including possibly by financing a third-party effort like No Labels, said the advisor.

A Haley campaign spokesperson did not respond to CNBC's request for comment before publication.

Trump is facing dozens of federal criminal charges, many related to his alleged efforts to overturn the 2020 presidential election. Nonetheless, the former president dominated the Iowa caucuses, winning more than 50% of support from caucusgoers.

Polls in New Hampshire do not predict Haley faring much better there than she did in Iowa. Trump leads in the Granite State primary by about 14 percentage points over Haley, according to a RealClearPolitics polling average.

A plethora of wealthy Republican-leaning donors have rallied around Haley as their alternative to Trump, even though he is still poised to capture the GOP nomination.

To keep the campaign going after New Hampshire, she will need their help, as well as any small-dollar donor money she can get, to try to fend off Trump in her home state of South Carolina. Trump is leading Haley in the South Carolina primary by 30 percentage points, according to a RealClearPolitics polling average.

Haley and her allied political action committee have spent more than $26 million on advertisements targeting New Hampshire voters, according to AdImpact. Trump and his allied PAC have invested more than $12 million on ads in the state.

Some Haley donors have already lost hope.

In Davos, Switzerland, a wealthy investment banking executive and Haley donor told CNBC on Tuesday that he's now convinced Trump will be the Republican nominee, and go on to defeat President Joe Biden in November.

The banker, advisor and lobbyist were granted anonymity to speak freely.

— CNBC's Alex Sherman contributed to this report.

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