Could Nikki Haley Really Beat Trump? Big Donors Are Daring to Dream.

Mr. Bush, a Republican who voted for Mr. Biden in 2020 and for Gary Johnson, the Libertarian candidate, in 2016, said he had been struck by her knowledge and poise.

“The topic that everyone is on is, ‘How do you beat Donald Trump?’” Mr. Bush said, “and she was careful to say, ‘Look, people will decide about him, but this is where I am on certain issues.’ And she rattled off some issues, related to our debt, related to our role in the world. But what you picked up was an electric energy,” he added, “that I think got this crowd really excited.”

But even with Ms. Haley’s momentum, halting Mr. Trump’s seemingly inexorable march to the Republican nomination promises to be a slog. With a wide edge in national and early-state polls, the former president is running effectively as an incumbent, with legions of supporters prepared to vote solely for him.

Several donors and advisers described two groups taking shape among the major, top-dollar donors:

First, those who have yielded to the likelihood that Mr. Trump, however they may feel about him, will probably be the nominee, and have decided to stop funding potential alternatives. Second, those who believe that with enough financial resources and a savvy field operation, Ms. Haley could unseat him.

Despite the long odds, her financial supporters say they see a path to victory.

“There were people that don’t like Trump at all but were very skeptical that he could be stopped,” said Eric Levine, a Republican fund-raiser who leads the bankruptcy and litigation practices at Eiseman Levine Lehrhaupt & Kakoyiannis. “They now believe he can be stopped,” he said, pointing to Ms. Haley’s steady climb in the polls.