Donald Trump speaks to supporters during a campaign rally in Poughkeepsie, New York, in April.EDUARDO MUNOZ/Reuters
On Tuesday evening, Cory Adair was watching television at his home in Mobile, Ala., when the results of the Indiana primary were announced. The former executive director of the state Republican Party in Nevada and Mississippi, Mr. Adair knew immediately what the results meant: Donald Trump would secure his party's nomination for president.
Hell, Mr. Adair thought, this is really happening. He headed to a local baseball game with his in-laws, but his mind was elsewhere. The party to which he had devoted his career was about to nominate someone he loathed. Should he vote for Hillary Clinton? Hope for a third-party candidate? Embrace a libertarian alternative?
Two days later, Mr. Adair still sounded shell-shocked, fumbling for words to describe his feelings. "I'm at a loss," he said. "It is really an emotional thing." He knew party leaders were doing their job by calling for unity, but "this isn't a normal election and Trump isn't a normal candidate."
A real estate mogul and reality-television star, Mr. Trump is now the presumptive Republican nominee for president, an outcome unimaginable only months ago. His victory presents his party's voters and officials with a bald choice: Support the most controversial nominee in recent history, or resist him and risk handing the White House to a Democrat.
The reaction to Mr. Trump's victory reveals a party roiled by dissent. Some lifelong Republicans publicly vowed to change their party affiliation, or even to vote for Ms. Clinton. Former presidents George H.W. Bush and George W. Bush said they would not attend the Republican National Convention in July, nor will Mitt Romney, the party's nominee in 2012.
Perhaps the most remarkable sign of the struggle with the new reality came from Paul Ryan, Speaker of the House of Representatives. Mr. Ryan said on Thursday that he was not yet ready to endorse Mr. Trump. The nominee would have to earn Mr. Ryan's backing. "I hope to support our nominee," Mr. Ryan said. "At this point, I'm just not there right now."
The extent to which Mr. Trump can mend these fractures and win over Republican donors, officials and operatives will help determine whether he has a chance in November. "We are in uncharted territory with a populist phenomenon," said Ron Bonjean, a Republican strategist and former senior Congressional aide. "It's going to be a while before there is a partial healing of the Republican Party."
Republican elected officials face a complicated choice, added John Green, a political scientist at the University of Akron. "Part of the calculus is, 'Is this guy going to get better as a candidate?'" he said. Republican politicians are thinking "very instrumentally" about how to deal with Mr. Trump, Prof. Green said. The debate is, "How much do we run away from him and how much do we get behind him?"
This week, some prominent Republicans threw their support behind Mr. Trump's candidacy, albeit with a notable lack of enthusiasm. They include figures such as Senate Majority Leader Mitch McConnell, Wisconsin Governor Scott Walker and Louisiana Governor Bobby Jindal. In September, Mr. Jindal memorably called Mr. Trump "a substance-free narcissist." On Tuesday, Mr. Jindal said he would vote for Mr. Trump, but "wasn't happy about it."
Some Republicans said reconciling themselves to Mr. Trump respects the will of voters. John Feehery, a Republican strategist in Washington, wrote in February that the party should reject Mr. Trump, likening his "authoritarian tendencies" to Nazi Germany and the Soviet Union.
Yet Mr. Feehery now plans to support him. "I'm not saying he's the perfect candidate," Mr. Feehery explained. "I've gone through the process of listening to voters and they are extremely frustrated." He mocked those Republicans swearing to leave the party or vote for Ms. Clinton. "They'll come back," Mr. Feehery predicted. "They'll find out that hanging out with socialists isn't that much fun."
But the Republicans who oppose Mr. Trump – because they believe he is not conservative enough, or that he is unfit to be president, or both – say they will not budge. Chip Griffin, a 42-year old conservative commentator in New Hampshire, vowed to change his party affiliation to independent after Mr. Trump's win in Indiana.
Mr. Trump "does not stand for the things that I stand for and he does not have the demeanour I expect in my leaders," Mr. Griffin said. "Frankly, straight up, he's a liar." Mr. Griffin will not vote for Ms. Clinton, but might write in a candidate in November or leave that line of his ballot blank. He sounded both wistful and bewildered. "I could never have envisioned not being able to vote for the Republican nominee," he said.
Ben Sasse, a Republican senator from Nebraska, has been vehement about not supporting Mr. Trump and explicit about his yearning for a third-party alternative. In a long Facebook post on Thursday, Mr. Sasse wrote that his voicemail was filled with messages from party bosses telling him that although Mr. Trump is awful, Republicans must support him because Ms. Clinton is the only other choice. "Why are we confined to these two terrible options?" Mr. Sasse asked.
At this late stage, mounting an independent bid for president is near impossible. Back in Alabama, Mr. Adair says he is going to research Austin Petersen, a candidate seeking the presidential nomination of the tiny Libertarian Party. But Mr. Adair's priority is thwarting Mr. Trump, even if that means doing something previously unthinkable: voting for Ms. Clinton.
Mr. Adair is worried it will take years for the Republican Party to recover from its run-in with Mr. Trump. "If we become the party of hate, if we become the party of anger, if we become the party who rejects anything other than white people, then I'm sorry, that's not what I signed up for," he said. "What a weird political world – and it's never going to be the same, I'll tell you that."