Republican presidential candidate Donald Trump said he will not take part in the Jan. 28 debate hosted by Fox News and Google, in part due to their choice to include moderator Megyn Kelly. (Reuters)

Donald Trump’s people announced Tuesday that he wouldn’t be participating in Thursday night’s Fox News-hosted GOP debate. “He’s definitely not participating in the Fox News debate,” campaign manager Corey Lewandowski told our colleagues at The Fix. “His word is his bond.”

His word, actually, is his bane. In the months since Fox News host Megyn Kelly asked Trump a tough question about his treatment of women at the Aug. 6 GOP debate in Cleveland, Trump has spread dumb and ill-founded complaints about Kelly on Twitter and elsewhere. Many of them contain a rude and sexist tinge. He has called her a “lightweight” and claimed that her popularity is linked to her months-long entanglement with Trump. “I might be the best thing that ever happened to her. Who ever even heard of her before the last debate?”

Fox News did the right thing as Trump escalated his threats. “Megyn Kelly is an excellent journalist, and the entire network stands behind her. She will absolutely be on the debate stage on Thursday night,” said Fox News chief Roger Ailes in a statement to The Post. And when Trump polled his Twitter followers about whether he should attend the Fox News debate, a Fox News rep issued this statement: “We learned from a secret back channel that the Ayatollah and Putin both intend to treat Donald Trump unfairly when they meet with him if he becomes president — a nefarious source tells us that Trump has his own secret plan to replace the Cabinet with his Twitter followers to see if he should even go to those meetings.”

Trump expressed contempt for the “wiseguy” Fox News statement.

Tempting though it is to game out the PR and political calculations between Fox News and Trump, there’s something bigger going down here. Momentous, even: The right-wing penchant for nonstop media criticism is swerving across the median, zigzagging around the road, about to wrap itself around that oak tree around the curve. Like other planks of the conservative canon — e.g., foreign-policy hawkishness — it has been invoked and ultimately abused by Trump. Such that it can no longer stand on its own.

See any good — or bad — conservative politician on the stump, and listen for the broadsides against the liberal mainstream media. They don’t give Republicans a chance; they distort things; they give weight to trivial stories that harm conservatives and ignore big stories that favor them — it’s a viewpoint that stretches back at least to a seminal anti-MSM speech by Spiro Agnew in 1969. Sometimes the gripes are well-placed; sometimes they are exercises in blame reassignment. The hard-working folks at NewsBusters keep a running compilation of the infractions and oddities. Have a look for yourself.

Into this tradition of media criticism stomped Trump’s presidential campaign. Whereas previous practitioners of the critique looked for quite specific signs of bias in the media, Trump has found bias or misconduct in just about anything that has been critical of him. He has railed against Politico for pointing out various truths; he has railed against CNN and just about every other broadcaster for the bias of not showing the full extent of his crowds; he has ripped pundits — and Post columnists — such as Charles Krauthammer and George F. Will for reasons that haven’t stuck with the Erik Wemple Blog; he has gone back and forth on whether Chuck Todd of NBC News is a nice guy; and so on.

All of which tees up the Kelly thing. “Megyn Kelly’s really biased against me,” said Trump in an Instagram video. “She knows that, I know that, everybody knows that. Do you really think she can be fair at a debate?” (Bold text added to highlight another clumsy Trump effort to co-opt a great conservative tradition.) Far from actually expressing any deep-seated animus toward Trump, Kelly’s bias bona fides consists of having asked Trump one killer question at the Aug. 6 debate:

Mr. Trump, one of the things people love about you is you speak your mind and you don’t use a politician’s filter. However, that is not without its downsides, in particular, when it comes to women. You’ve called women you don’t like “fat pigs, dogs, slobs, and disgusting animals.” Your Twitter account . . . has several disparaging comments about women’s looks. You once told a contestant on ‘Celebrity Apprentice’ it would be a pretty picture to see her on her knees. Does that sound to you like the temperament of a man we should elect as president, and how will you answer the charge from Hillary Clinton, who was likely to be the Democratic nominee, that you are part of the war on women?

After struggling with that question, Trump fretted that Kelly and Fox News were tougher on him than on his competitors. Another way of looking at it: Kelly was repeating his own statements, and it was really tough to listen to.

The ironies here are circular. Over the years, Fox News has boosted its own ratings by frequently airing accusations of media bias. Now its ratings — at least for Thursday night’s debate — stand to suffer over just such an accusation. Everyone tunes in to see just how Trump will bring out the worst in those who surround him. And the National Review got tossed from hosting a February debate because it dared to exercise its prerogative as an opinion journal to editorialize against Trump.

Fox News, of course, will be fine; it has ruled cable news ratings for the last decade and a half and will continue doing so. Trump, of course, will be fine; he has money and insouciance and ignorance. Media criticism, though, may need a round or two of therapy.