A ghastly pall has descended over U.S. politics. Barring a minor miracle, Donald Trump really will be running against Hillary Clinton to be president.

The world is looking on in slack-jawed horror. Never in our lifetime has a man so unsuitable for office got so near the White House. Almost no one saw it coming – certainly not the Republican establishment, and least of all the pundits, who've been reassuring us for months that this clownish, vulgar reality-TV star would never, ever get near the nomination.

How could this happen? New Yorker editor David Remnick, who is in a state of shock, blames the people. As he told Politico, Mr. Trump's success reflects an "ugliness" that appeals to "every worst instinct" in America. Nicholas Kristof, the New York Times columnist, says Mr. Trump has "shrewdly manipulated the news media."

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But it's not entirely the people's fault, or the media's fault. The Republican establishment has been out of touch for years. It offers a brand of conservatism that people don't care about or else have actively rejected. Unlike their leaders, most Republican voters don't care all that much about constitutional purity. Many of them are are middle-class or lower. They don't want tax cuts for the rich. They want their health care and social security to be protected. They think there's too much uncontrolled immigration. They're tired of senseless foreign wars in far-off places where everybody hates the United States anyway. They care a lot less than party leaders if other people want to get abortions.

As David Frum so brilliantly put it, the Republican establishment is promising fewer benefits, more immigration and more foreign wars. Mr. Trump is promising more benefits, less immigration and fewer foreign wars. As The Washington Post's Charles Lane puts it, "Trump wants to make America more like Denmark."

Mr. Trump's basic policy positions (so far as they're discernible) are not all that bizarre. The problem is that he's unfit to govern. The problem is his character, his temperament and his judgment, as well as his authoritarian leanings, his rage, his bullying, his tactics of threats and intimidation, his history as an unsavoury businessman, his appeals to bigotry, his narcissism, his vengefulness, his erratic nature, his vulgarity, his recklessness, his deceit, his utter ignorance of government and of world affairs, and his contempt for the first amendment (the one about free speech).

He's a human wrecking ball. And that's another reason people like him. They want to stick it to the political class.

If it survives, the GOP will never be the same again. That's probably a good thing. Meanwhile, the party is in meltdown. Insiders are invoking the five stages of grief – from denial, anger and bargaining to resignation and acceptance – to describe the party's plight. Some neocons, still in deep denial, are penning desperate screeds about how Mr. Trump can still be stopped. But time is running out. His opponents are fractured and show no sign of joining forces. (Besides, Ted Cruz may be less electable than Mr. Trump.) A round of winner-take-all primaries starts on March 15, which means that Mr. Trump could soon have the nomination all sewn up.

"It is too late," Alex Castellanos, a Republican media strategist, told The Washington Post. "There is a fantasy effort to stop Trump … but it exists only as the denial stage of grief."

Republican politicians and operatives are now facing a moral test of their own: Should they sacrifice their principles to support a raving demagogue, or repudiate him and work for his defeat – even if they'll be exiled into outer darkness? Just watch the naked agony of Chris Christie as he swears fealty to the new mob boss. The sight of so many people scrambling to calculate their own best interests won't be edifying.

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The Democrats are watching their enemy's implosion with great glee. Perhaps they shouldn't be. Mr. Trump's drawing power is deeper and more diverse than anyone expected. His appeal isn't just to the disaffected white working class – he's reaching more educated folks, and also Democrats. His views on military adventurism (he called the Iraq war "a big, fat mistake"), globalization and free trade (China is killing us) resonate across party lines.

Another thing is working in his favour. Even in some of the less crazy, less extreme parts of the United States, it's no longer shameful to admit you like Mr. Trump. And once that taboo is broken, more and more people will come out and say it.

I still think Hillary Clinton will win. (Frankly, it's too scary to think she won't.) But she is going to have a turnout problem. Millions of Democratic voters, especially African-Americans, will probably be too indifferent to show up. Her e-mail scandal isn't over. And Mr. Trump has mastered the art of of extreme fighting – a form of combat in which anything goes.

Trust me. This won't be pretty.