Was last week beginning of end for Trump?

“It’s not like in the movies,” is good advice for almost any field or endeavor, from war to Wall Street. But perhaps nowhere is it more true than in politics.

At the end of “Mr. Smith Goes to Washington,” Claude Raines admits he was the villain all along. Lonesome Rhodes, the populist demagogue played to perfection by Andy Griffith in “A Face in the Crowd,” has a hot-mic moment on TV and the audience gets cathartic release seeing his schemes fall apart.

Six years ago, I predicted that many conservatives would, like Alec Guinness’ Col. Nicholson in “The Bridge on the River Kwai,” have an epiphany about their misguided role in abetting Trump. “I don’t know whether Trump will win the nomination or the presidency,” I wrote. “But I am fairly certain that if he does, a great many people will one day say, ‘My God, what have I done?’ ”

I wasn’t entirely wrong, but I was wrong in the ways that matter.

It was Gen. Douglas MacArthur who popularized the British saying, “Old soldiers never die; they just fade away.”

What’s true of old soldiers is also true of most demagogues. Sen. Joseph McCarthy served more than two years after his censure, a broken morphine addict, but with ample supporters nonetheless. Father Coughlin, the antisemitic “radio priest,” remained a parish pastor for another quarter century after he lost his microphone in 1940.

Political movements have a half-life; it’s impossible to predict how long they will last. What’s clear is that Donald Trump’s has kicked in.

A month ago, the Washington Examiner editorialized that Trump was unfit for office. The Examiner’s owners shuttered the Weekly Standard at least in part because of its opposition to Donald Trump.

Last Friday, the Wall Street Journal and the New York Post, both owned by Rupert Murdoch, declared Trump should fade away. The Post wrote in an editorial that “as a matter of principle, as a matter of character, Trump has proven himself unworthy to be this country’s chief executive again.”

The Journal echoed the sentiment: “Character is revealed in a crisis, and Mr. Pence passed his Jan. 6 trial. Mr. Trump utterly failed his.”

Some would argue it shouldn’t have taken Jan. 6 to grasp Trump’s character, but that misses the point.

Trump’s hold on the right is in the process of terminal decay.

On Friday night, when Trump was haranguing rallygoers about the House Jan. 6 committee, Murdoch-controlled

Fox News was running an interview with Florida Gov. Ron DeSantis.

Trump’s endorsements can still matter, particularly in crowded primaries. But they often fail to make the difference, as in Georgia, where some of Trump’s most hated Republicans — Gov. Brian Kemp and Secretary of State Brad Raffensperger — won handily. In other cases, his endorsements are lagging indicators; he picks the inevitable winner because they are inevitable.

A recent New York TimesSiena College poll sent shockwaves throughout Washington, showing Joe Biden’s presidency to be on life-support. It was brutal in every regard save one:

Despite being wildly unpopular with Democrats, Biden still beat Donald Trump in a head-to-head match-up.

There’s a lot of handwringing over whether Trump will announce his candidacy for another presidential run before the 2022 midterms.

This is no trivial thing — Trump could still win the 2024 GOP nomination.

But it is worth recognizing that this gambit is not a sign of strength, but of growing weakness.

Trump sees the tide going out as his former loyalists depart without him and is desperate to raise sail before it is too late.

Polls of Republicans can be misleading. Yes, he still has diehard supporters, but a lot of Republicans — voters and politicians — would rather just move on than admit they were wrong.

One explanation for Murdoch and others turning on Trump is that they recognize he could cost the GOP dearly in the midterms.

Another explanation: to signal to Trump he can’t expect a coronation and to donors and Republican politicians that there is room to break from him. A lot of White House hopefuls have gotten that message.

What’s missing from all of this is any meaningful admission — never mind atonement — for the role many played in creating Trump in the first place.

Passionate opponents of Trump want that satisfaction, but they will never get it.

Instead, the most likely scenario is that in a few years, many of Trump’s former accomplices, apologists and abettors will simply marvel at the strange chapter they helped author and pretend they had nothing to do with it. Because politics doesn’t work like it does in the movies.