Donald Trump is a racist, a nativist, a demagogue, someone who threatens the American Dream. He is an unstable egomaniac who should not be trusted with his country's nuclear arsenal. He would turn the world's entire Muslim population against the United States, making the world a more dangerous place.

And if you're any of the top Republicans who have described him in exactly these terms, he's still your guy.

At least he was until a terrorist slaughtered 49 people in an Orlando nightclub, and the presumptive Republican presidential nominee's reaction was to congratulate himself for predicting something like this would happen, double down on a promise to discriminate against all practitioners of the terrorist's religion and imply that the current President is on the terrorist's side.

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There was nothing surprising about Mr. Trump's response to what happened in Orlando, if you watched him in his twelve months as a presidential candidate leading up to it – like his fellow Republicans evidently did, since they attached all those above descriptors before the massacre. But as the U.S. media lit up last week with stories of leading GOP figures distancing themselves from him – openly admonishing him, or running down hallways to avoid reporters' questions about him – one got the sense that people who have gone down the road of supporting someone they believe is genuinely dangerous recognized one of their last available off-ramps.

You have to hope they take it, for their sake if not the sake of their country and the rest of the world.

Among the most stomach-turning aspects of this U.S. election year is how powerful people, who presumably started their career in public life with noble intentions to serve, have confirmed the worst stereotypes of politicians being feckless, opportunistic and blindly partisan.

There are people who accidentally wind up on the wrong side of history. Then there are these guys – from former presidential candidates to congressional leaders to high-profile governors – who seem to know they're on the wrong side of history, but can't help themselves because Mr. Trump is wearing their party's colours and there could be career downside to going against him.

New Jersey Governor Chris Christie has come in for a special amount of ridicule for running against Mr. Trump for the nomination, then becoming a weirdly sycophantic supporter after Mr. Trump steamrolled him. As Mr. Christie has awkwardly stood by the object of his affection at public events where Mr. Trump has mocked him for his political record or his obesity – a New Yorker article last week described Mr. Christie as "a sort of manservant" and claimed he was caught fetching Mr. Trump's McDonald's order – fellow Republicans have probably thought to themselves, at least I'm not that guy. But it should hardly feel much more noble to be Paul Ryan, the House Speaker and purported conservative thought leader, acknowledging Mr. Trump is guilty of "the textbook definition" of racism for suggesting a judge cannot do his job because of his Mexican heritage, then in the next breath saying he supports him because he thinks there could be "common ground on the policy issues of the day."

Or Marco Rubio, who stands by his description of Mr. Trump when he was running against him as "an erratic individual" who "should not be trusted with the nuclear codes of the United States," but has now endorsed him because he pledged to support whoever wound up being the nominee.

Or former Texas governor Rick Perry, who described Mr. Trump as a "cancer on conservatism" who would lead Republicans "down the road to perdition," and now says he'd be happy to serve as his vice-presidential pick.

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John McCain, the former presidential nominee and war hero who Mr. Trump decried as a loser for having been captured and tortured in Vietnam, perhaps best encapsulates this feebleness. He has not been quite as apocalyptic in his warnings about Mr. Trump, merely getting caught on tape lamenting that his "nativism" will hurt Republicans with Hispanic voters. But it is impossible to believe the hawkish Arizona senator would sincerely prefer the isolationist Mr. Trump – who isn't sure the United States should remain in NATO and admires Vladimir Putin – to the more interventionist Hillary Clinton.

Mr. McCain is 79 years old, and if his political career isn't yet in its twilight, it's awfully close. But he apparently can't stomach the idea of jeopardizing another six years in the Senate by incurring the wrath of Mr. Trump's millions of fans, or else he's just been partisan so long that some perverse sense of loyalty requires him to rally behind the nominee.

Last month, he chastised the few elected Republicans wavering from supporting Mr. Trump for being "foolish" in ignoring the will of the people; last week, he appeared to wholeheartedly embrace Trumpism by accusing Barack Obama of being "directly responsible" for the Orlando attack because he had not done enough to fight the Islamic State.

After going off the deep end like that, it may be too late already for Mr. McCain to preserve his dignity. Some of his colleagues may still have more of a window.

They needn't join efforts to somehow nominate someone else at next month's Republican National Convention, which might go too far in thwarting voters' will even if it were somehow possible. They could merely say what should be obvious: that since they plainly believe Mr. Trump would be a disastrous president, they don't intend to vote for him and won't encourage others to do so.

But that window is rapidly closing. There's still a chance, as of now, that Mr. Trump could win the presidency. If polls eventually show that chance has evaporated altogether, it will be easy for other Republicans to pull back their endorsements. The thing about being on the right side of history is that it only matters before that history has been written.