When ads supporting Mr. Vance began to run, he gained traction, though he still trailed. By April 4, his super PAC posted a memo saying Mr. Vance was no longer “primarily associated” with his prior criticisms of Mr. Trump.
“J.D. showed a lot of resilience in this race — and when the political class in the Beltway wrote him off as dead in the water earlier this year,” said Andy Surabian, who, along with Jai Chabria, ran Mr. Vance’s campaign.
Indeed, Mr. Trump was swayed in part by how Mr. Vance handled himself on television. In one debate, when Mr. Mandel and Mr. Gibbons went toe to toe, Mr. Vance scolded them, rising above the fray — and impressing Mr. Trump.
Mr. Trump was on a golf course, editing his statement endorsing Mr. Vance, when NBC News reported he was about to issue it. Some of Mr. Trump’s advisers, working with Mr. Vance’s opponents, were lobbying the former president not to, but the report only solidified his decision.
Mr. Vance also benefited from a more accurate picture of the electorate.
Mr. McIntosh, of the Club for Growth, repeatedly argued to Mr. Trump that the former president’s pollster, Anthony Fabrizio, who was also working for Mr. Vance, had modeled the Ohio primary electorate inaccurately.
The Club for Growth’s polling last weekend showed Mr. Vance receiving 26 percent of the vote. Mr. Fabrizio’s polling had Mr. Vance at 32 percent.
Mr. Vance finished with 32.2 percent.
Jeff Roe, a Republican strategist who worked with the Club for Growth in Ohio, called Mr. Trump before the polls closed on Tuesday to concede. He told Mr. Trump that the former president was “100 percent responsible” for Mr. Vance’s win, according to a person briefed on the conversation.
In his victory speech Tuesday night, Mr. Vance thanked, among others, Donald Trump Jr., Charlie Kirk, Tucker Carlson and, of course, the former president.
Shane Goldmacher reported from Cincinnati, and Maggie Haberman from New York.