Nikki Haley lost Iowa. Then she lost New Hampshire. Now, some of the biggest donors in the Republican Party — a Trump-resistant donor class that has fueled her candidacy for months — are at least opening the door to former President Donald J. Trump.

A network of some of the country’s wealthiest Republican donors gathered this week at a Florida winter meeting held by the American Opportunity Alliance and heard from top aides to both Mr. Trump and Ms. Haley. The gathering on Monday and Tuesday was one of the first significant steps in the reluctant drag back to the reality of Mr. Trump for some of these donors, after aides to Mr. Trump received no such invitation to the group’s fall retreat.

Ms. Haley has a series of fund-raisers in the coming days, and held one in New York City on Tuesday night. Money will not be an obstacle for her candidacy. But privately, some of the party’s major donors — including some who are supporting Ms. Haley — say they are ready for the contest to come to an end, in order to focus on President Biden, and concede that Ms. Haley has little chance of overtaking Mr. Trump absent some unforeseen event.

At the American Opportunity Alliance retreat, Ms. Haley had far more backers than Mr. Trump did. Kenneth Griffin, a billionaire hedge-fund executive and major Republican donor who attended the retreat, gave $5 million to her super PAC this month, according to a person close to him.

Before Gov. Ron DeSantis of Florida dropped out of the race, he and his allies had anticipated support from Mr. Griffin because the investor had given generously to him in the past. But Mr. Griffin was disappointed by what he saw as an incompetent campaign coupled with profound policy mistakes, such as Mr. DeSantis’s description of Russia’s invasion of Ukraine as a “territorial dispute,” according to several people familiar with his thinking.

Mr. Griffin had been holding out for a younger candidate who could challenge Mr. Trump, and it took him months to decide to support Ms. Haley. He praised Ms. Haley in a statement to reporters, saying that “America would be well served by someone with her foreign policy credentials and policy priorities in the White House.”