PRESIDENT TRUMP told the nation Sunday it was all “Fake News.” Reports were swirling that Nick Ayers, who leads Vice President Pence’s team, had been in line to become the next White House chief of staff, only to decline when Mr. Trump offered him the job. Perhaps unhappy with stories revealing the continuing disorder in his administration, the president attacked the messenger.

Unfair? Made up? Fake news? Go back almost exactly one year. Similar stories were published about Mr. Trump’s feelings toward then-Secretary of State Rex Tillerson, reporting that the president was preparing to fire Mr. Tillerson and replace him with then-CIA Director Mike Pompeo. All lies, Mr. Trump insisted. “The media has been speculating that I fired Rex Tillerson or that he would be leaving soon - FAKE NEWS!” the president tweeted on Dec. 1, 2017. “He’s not leaving and while we disagree on certain subjects, (I call the final shots) we work well together and America is highly respected again!”

Mr. Trump dismissed Mr. Tillerson and replaced him with Mr. Pompeo a few months later. And last week, after Mr. Tillerson criticized the president for his lack of discipline and disinclination to read, Mr. Trump said that the two of them did not have a good relationship, after all. Mr. Tillerson “didn’t have the mental capacity needed. He was dumb as a rock and I couldn’t get rid of him fast enough. He was lazy as hell,” Mr. Trump tweeted Friday.

We are left with two options. Either Mr. Trump was lying last year, when he disparaged reports of his unhappiness with Mr. Tillerson as fake news. Or he is lying now, when he says he couldn’t get rid of his former secretary of state fast enough. Given that he fired Mr. Tillerson just as the reporting had predicted he would, we can be pretty confident that the initial stories were correct.

The only thing fake in all this has been Mr. Trump’s insistence that reporters got it all wrong — the same claim he is making now about the stories on his chief-of-staff vacancy, the same claim he makes about practically any article he does not like. We cite this clear case study for a reason. When Mr. Trump deflects unwelcome news by disparaging the media, he does real damage. It may serve his political purpose to propagate the notion that journalism can never be trusted. But he is wrong, and his corrosive cynicism harms the nation.