No wonder Trump won’t show up on a debate stage. He’s gotten to where he can barely keep it together in front of the adoring throngs at his campaign rallies. Somewhat smaller throngs, it must be said — but, hey, it’s January, and everybody’s seen The Trump Show many times by now.

Even so, that was a real humdinger the great man emitted the other day when he confused Nikki Haley with Nancy Pelosi, blaming her for failing to provide adequate security during the Jan. 6 riot. Psychiatrists call it “decompensating.” Ordinary people call it “losing your marbles.”

Courtesy of Michael Tomasky in The New Republic, here’s a transcript of what Trump said: “By the way, they never report the crowd on Jan. 6. You know, Nikki Haley, Nikki Haley, Nikki Haley ... you know they ... did you know they destroyed all of the information, all of the evidence, everything, deleted and destroyed all of it? All of it! Because of lots of things. Like Nikki Haley is in charge of security. We offered her 10,000 people. Soldiers, National Guard — whatever they want. They turned it down. They don’t wanna talk about that. These are very dishonest people.”

That’s right, sports fans, Trump confused the then-Democratic speaker of the House with his Republican presidential rival and former United Nations ambassador. Not once, but several times. All in service of one of his most absurd lies: that he offered Speaker Pelosi soldiers to defend the U.S. Capitol from the same mob he’d urged to “fight like hell, or you won’t have a country anymore.”

Also to support another lie: that the House Select Committee that investigated the events of Jan. 6 possessed this exculpatory evidence but destroyed it. Yeah, sure they did. And all of Humpty Trumpty’s horses and all of his men couldn’t put it back together again.

In reality, numerous White House aides testified that Trump spent hours enjoying the spectacle on TV, even as they begged him to call off the mob. Then at 2:24 p.m., with the crowd having erected a gallows and chanting “Hang Mike Pence,” Trump sent out a tweet: “Mike Pence didn’t have the courage to do what should have been done to protect our Country and our Constitution.”

That is, to prevent the Electoral College vote and award the election to Trump. The election he’d lost by 7 million votes.

But, yeah, it was all Nikki/Nancy’s fault.

And if you believe that ... Well, what won’t you believe?

Tomasky asks an interesting question. If Haley herself hadn’t made an issue of Trump’s senility, would the news media even have covered the event? Probably not. They’ve been ducking it for months, even as the deterioration in the former president’s affect has grown steadily clearer.

Here’s the self-proclaimed “stable genius” on the topic of wind turbines, which he claims are driving whales crazy: “I never understood wind. I know windmills very much. ... Gases are spewing into the atmosphere. You know we have a world, right? So the world is tiny compared to the universe. So tremendous, tremendous amount of fumes and everything.”

Now I don’t want to brag, but I could never get that drunk. But of course, Trump famously doesn’t drink. Instead, he boasts about acing a screening test for dementia. Going on six years ago.

If Humpty Trumpty were a doctor, lawyer, a veterinarian or a hairstylist, his clients would tiptoe quietly away. A presidential candidate, however, is to many people a fantasy figure — a combination sideshow barker and shaman, credited in the popular mind with powers he does not and never will have. So, it’s not a practical decision. Tribal loyalties are involved.

During my lifetime, the most astonishing example of mass psychosis I’ve seen was the Jonestown Massacre of hundreds of religious devotees by suicide — the origin of the phrase “drinking the Kool-Aid.” Second was the Branch Davidian catastrophe in Waco, Texas, where evidence showed cult leader David Koresh helped massacre his followers.

No, Trump’s MAGA movement is nowhere close. Even so, it’s going to be interesting to see how his followers react as his psychological and intellectual decompensation proceeds under the enormous pressure of a presidential campaign and a series of criminal trials.

Tomasky points out that given the media obsession with Joe Biden’s age — Fox News and others televise his every verbal or physical stumble relentlessly — for the president to commit anything like Trump’s Nikki/Nancy blunder would probably result in his being forced to withdraw.

And properly so, as far as I’m concerned.

Anybody who’s ever had a relative or close friend disappear over the event horizon into dementia knows the story. Trump will have better days and worse days, but it’s a one-way journey to nowhere.

Meanwhile, it’s not the MAGA faithful that scare me; it’s the cynics and opportunists who think they can flog him across the finish line.

Arkansas Times columnist Gene Lyons is a National Magazine Award winner and co-author of “The Hunting of the President” (St. Martin’s Press, 2000). You can email Lyons at eugenelyons2@yahoo.com.