Even by Donald Trump’s standards, his tweet of Oct. 23 — the one that called NeverTrumpers “human scum” — plumbed new depths in the debasement of presidential speech.

But what else has changed? If Robert Ballard, who discovered the wreck of the Titanic, were given the job of finding Trump’s moral bottom, he’d fail.

Far more revealing in Trump’s tweet was its first sentence. “The Never Trumper Republicans, though on respirators with not many left, are in certain ways worse and more dangerous for our Country than the Do Nothing Democrats,” the president wrote, before warning of their scummy natures.

Think that one over. If the few remaining NeverTrump conservatives can still be that dangerous while we’re on respirators, we must be powerful indeed. Somewhere in eternity’s permanent exile, Leon Trotsky is smiling.

Yet Trump’s tweet is basically right on both counts. As a movement, NeverTrumpism is on life support. And the president has greater reasons than ever to fear it.

Three years ago, on the eve of the election, the NeverTrump coalition was a wide one, ranging from hard-core conservatives like Erick Erickson and Ted Cruz to somewhat squishier ones like Michael Gerson, John Podhoretz and, well, me.

Then Trump won. The guy who was supposed to lead his party to a catastrophic defeat became the man who, in the eyes of the right, uniquely figured out how to save the country from Hillary Clinton. The coarseness of speech and crudeness of character that were supposed to be his central flaws became evidence of his gutsy indifference to liberal reproach.

There were also those conservative policy and political victories. Regulatory rollback. Gorsuch, Kavanaugh and all the lower court judges. Increased military spending. The tax cut. Withdrawal from the Iran deal. An expanded GOP majority in the Senate. The Mueller fizzle.

The NeverTrumpers scattered. Some became ex-conservatives. Others, full-on Trumpers. Still others, anti-anti-Trumpers — which only meant they were smart enough to see the president for what he is and churlish enough to be angry at those who wouldn’t join them in capitulating to it.

Yet the NeverTrumpers never scattered entirely, and thank heavens for that. Every political system will always have a conservative faction, and every healthy democracy needs that faction to be rooted in some combination of classical liberalism and moral traditionalism. Trump’s GOP, whatever its political fortunes, is the opposite: a nativist party led by a libertine.

At some level, conservatives know this. Trump knows they know it. Which explains why he has turned his sights on NeverTrumpers: What despots and demagogues fear most is their followers developing a conscience.

No wonder the president chose to lambaste Lt. Col. Alexander Vindman as a “Never Trumper.” The combat veteran had the simple decency of being scandalized by what he heard from the president on the Ukraine phone call, and by what he knew of the discrepancies between what he heard on the call and the account of it released by the White House.

The decency of being scandalized is what being NeverTrump is centrally about, and why the movement remains important. It’s the opposite of the opportunism required to go along with the president because you might get something out of him.

It’s the same sense of scandal that led to the first significant GOP revolt against Trump since John McCain turned his thumb down on Obamacare repeal in 2017: the suppurating disgust even pliant conservatives like Mitch McConnell and Lindsey Graham feel at Trump’s cavalier betrayal of the Kurds. It could motivate John Bolton (a born-again NeverTrumper, along with John Kelly, Rex Tillerson, H.R. McMaster, Anthony Scaramucci and everyone else who made the mistake of working for this president) to deliver what may yet be the most devastating insider’s indictment of the president’s shameless shadow foreign policy.

And it helps explain why the president’s support with his base is slipping at last. A new poll finds Trump’s support among Republicans at 74% — an 8-point decline since September and the lowest since he was elected. Nearly 1 in 5 Republicans support impeachment and removal. So do 47% of independents. These numbers will not move in Trump’s favor if the truth about his drug deals (to borrow Bolton’s phrase) continues to come to light.

I doubt any of this will be sufficient to get at least 20 Republican senators to vote for Trump’s removal from office. But Trump knows that the number needed to spell his moral defeat on impeachment is four. If Mitt Romney, Susan Collins, Lisa Murkowski and one other Republican join the Democrats to convict, the political humiliation will be thunderous. And, as my colleague David Leonhardt has convinced me, it could devastate his re-election chances. If the administration thinks impeachment is such a political winner, they wouldn’t be fighting it this hard.

In the meantime, someone ought to print “Human Scum” on a limited-edition T-shirt. Given who said it about whom, it turns out to be a badge of honor.

Bret Stephens | The New York Times, (Tony Cenicola/The New York Times)

Bret Stephens is an Op-Ed columnist for The New York Times.