But in a Wall Street Journal op-ed article this week, Mr. Jindal was singing a different tune about Mr. Trump. Explaining why he would vote for the party’s new standard-bearer, he said that Hillary Clinton would be a far scarier alternative. “I do not pretend Donald Trump is the Reaganesque leader we so desperately need, but he is certainly the better of two bad choices.”

Other establishment figures are also coming around faster than some expected. Senator Orrin G. Hatch, Republican of Utah, publicly endorsed Mr. Trump without hesitation after their meeting on Thursday in Washington. Sheldon Adelson, the casino mogul and passionate pro-Israel advocate, endorsed Mr. Trump in a Washington Post op-ed article on Friday.

“You may not like Trump’s style or what he says on Twitter, but this country needs strong executive leadership more today than at almost any point in its history,” Mr. Adelson wrote, calling on all Republicans to coalesce behind him.

While critics such as Mitt Romney have continued to speak out against Mr. Trump, much of the “Never Trump” contingent seems to have gone quiet. For them, there is 2020 to think about, and those who disapprove of the candidate might not want to be seen as having helped Mrs. Clinton win the presidency if she defeats Mr. Trump in November.

“The biggest uniting force in the Republican Party is the prospect of a Hillary Clinton presidency,” said Ryan Williams, a political consultant and former spokesman for Mr. Romney. “That is a motivating factor in mollifying even some of Mr. Trump’s harshest critics.”

Still, for those who fought the hardest against Mr. Trump, making peace will not come easy.

Senator Marco Rubio stood by his pledge to support the Republican nominee in an interview with CNN this week, but he struggled to reference Mr. Trump by name and said that his concerns about his former rival continue to apply.

The wounds appeared to be most fresh for Mr. Cruz, who until last week was hoping to capture the nomination at a contested convention. He said in a radio interview on the “Michael Berry Show” on Thursday that he still plans to go to Cleveland July 18-21 to cheer on the delegates, but it was clear that the ill will toward Mr. Trump has not subsided.