If Donald Trump wins the Republican Presidential nomination, will the conservatives who have sworn that they would never vote for him actually turn to Hillary Clinton? Photograph by RJ Sangosti / The Denver Post via Getty

The completion of Donald Trump’s hostile takeover of the Republican Party is now within reach. If a lot goes right for Marco Rubio, he has a narrow shot at defeating Trump—Karl Rove and David Wasserman have their own detailed explanations—but Trump, after winning three out of the first four contests and demonstrating that he appeals to a wider and growing swath of the Republican electorate, is the overwhelming favorite. Prediction markets now put the odds of Trump securing the G.O.P. nomination at seventy-four per cent.

The historic nature of a Trump victory can hardly be overstated. He could very well stand at a lectern in Cleveland at the Republican National Convention, in July, accepting the nomination of a party whose top elected officials—governors, congressmen, and senators—have either refused to support him or actively opposed his nomination. Yes, there are some cracks. This week, two House members endorsed Trump, and other elected officials will surely jump aboard, especially those representing Trump strongholds. “A lot of our base is supporting Donald Trump,” South Carolina Congressman Mick Mulvaney told me late last year, during negotiations over the budget.

But Trump represents such a radical break with the Republican consensus on important issues that a significant segment of the Party will never back him. Among the Party’s intellectual and strategist class, the number of figures on the anti-Trump right has been growing in recent weeks in direct proportion to Trump’s successes.

The strongest resistance to Trump comes from the foreign-policy establishment of the Republican Party. Bill Kristol, the editor of The Weekly Standard, which is best known for its advocacy of a hyper-interventionist foreign policy, told me that there was no chance he would ever back Trump. “I've been Sherman-esque—and more!,” he said in an e-mail, “since I've said I would try to recruit a real conservative to run as a fourth (Bloomberg being the 3rd) party candidate.” He added (without irony, I think) that “Dick Cheney-Tom Cotton would be the ideal ticket, but am working on others that approach that high level.”

Eliot Cohen, a professor at Johns Hopkins University’s School of Advanced International Studies and a former State Department official in the second Bush Administration, recently tweeted his “short list” of reasons he would never back Trump: “demagoguery, torture, bigotry, misogyny, isolationism, violence. Not the Party of Lincoln & not me.”

Some conservatives who care about foreign policy above all other issues view Trump himself as a national-security threat. Bryan McGrath, a conservative blogger and former Navy officer, recently posted the text of the oath he took when he was sworn into the Navy, in which he swore to “defend the Constitution of the United States against all enemies, foreign and domestic,” and wrote, “Because I view Donald Trump as domestic threat to the internal stability and external security of the United States, I cannot be faithful to this oath and vote for him.”

Similarly, in an editorial in the Times, titled “Why I Will Never Vote for Donald Trump,” Peter Wehner, a top adviser to George W. Bush, wrote, “Mr. Trump is precisely the kind of man our system of government was designed to avoid, the type of leader our founders feared — a demagogic figure who does not view himself as part of our constitutional system but rather as an alternative to it…. For this lifelong Republican, at least, he is beyond the pale. Party loyalty has limits.” (Wehner was careful to add that he would not support Hillary Clinton or Bernie Sanders.)

Other conservatives point to Trump’s liberal past as the main reason for their opposition. “I have become convinced that Donald Trump’s pro-life conversion is a conversion of convenience,” the radio host Erick Erickson recently wrote. “Life is the foremost cause in how I vote. Therefore I will not be voting for Donald Trump at all. Ever.”

Charles Murray, the political scientist best known for writing “The Bell Curve,” and whose last book, “Coming Apart,” was about the struggles of the white working class, told me in an e-mail that he too was inalterably opposed to supporting Trump, but he said the main issue was not so much Trump’s ideology as his character:

It’s like Wolfgang Pauli’s famous crack, “That is not only not right, it is not even wrong.” He doesn’t even have a bad character. People with bad characters can have strengths. As far as I can tell he has no character. He’s a bully with subordinates. He does business in ways that good businesspeople despise—and he’s not even very good at that. He says things about people, especially his wives, that are so obnoxious that calling them obnoxious doesn’t come close to how awful they are. He constantly lies about things that can be checked. He brags incessantly—really unattractive in itself—but he doesn’t even brag about things that he could appropriately be proud of. The guy is pathetic.

The oddest thing about his popularity with white middle-class and working-class males is that if he lived next door to them, they would despise him.

Several Republicans in the Party’s consultant class, especially the more libertarian-leaning members, have also vowed that they would never back Trump. Liz Mair, a former Republican National Committee staffer who is running a cash-strapped anti-Trump super PAC, wrote to me, “I have repeatedly stated that if he is the GOP nominee, I will either vote third party or do a write-in, potentially of myself. At least if I do the latter thing, I know I’m voting for someone I 100% agree with for once :)” She is joined by Rick Wilson, who, judging by his Twitter feed and other commentary, is the Republican who is having the most fun attacking Trump. “I will continue to oppose Trump, implacably and unceasingly,” Wilson recently wrote in one of the more over-the-top contributions to the no-Trump-ever canon. “I will not bend. I will not cease this fight. I will never embrace this thuggish, venal, gibbering psychotic, and I will not countenance those who do. I don’t care if I’m the last Republican in America standing to resist this man, but with almighty God as my witness, I will not vote for Donald Trump.”