Metals magnate Andy Sabin said in an interview late on Wednesday that the Republican race was now essentially over. Trump has a prohibitive lead in national opinion polls.

"Haley needs to drop out," Sabin said. "Regardless of what anyone tells you, her money is going to dry up. Why would you fund someone who you know has no chance?"

Trump's back-to-back wins in the Iowa and New Hampshire contests have made his march to the Republican nomination almost certain as he looks ahead to a likely general election rematch with Democratic President Joe Biden in November.

Haley, Trump's last surviving Republican rival, is refusing to bow out, triggering a warning to her donors from Trump on his social media account on Wednesday night.

On the Truth Social app, Trump said anybody making a contribution to Haley would be "permanently barred" from his political orbit.

Haley responded on social media platform X with a link to donate to her campaign: "Well in that case ... donate here. Let's Go," she wrote.

Trump is keen to knock Haley out of the Republican nominating race before the next major contest, in South Carolina - Haley's home state - on Feb. 24. Threatening her donors is just one tactic he and his campaign are using to pressure the former South Carolina governor to quit.

Another major Haley donor, Reid Hoffman, the billionaire co-founder of online business and employment platform LinkedIn, also does not plan to keep funding her campaign, according to CNBC.

Dmitri Mehlhorn, a Hoffman adviser, said Haley no longer had a path to the nomination.

"The only way I can see (a path) happening is if Trump has a 'senior moment,' and she's able to exploit it to persuade GOP voters that he's lost it," Melhorn said.

To be sure, Haley retains support among some donors. Retail businessman Art Pope said he was still backing her bid.

(Reporting by Alexandra Ulmer in San Francisco and Tim Reid in Washington; editing by Ross Colvin and Jonathan Oatis)

By Alexandra Ulmer and Tim Reid