Donald Trump ascends the stairs with his fist raised after opening the Trump Taj Mahal casino-hotel in a show of fireworks and laser lights in Atlantic City in April 1990. (Charles Rex Arbogast/Associated Press)

Henry Allen is a former Post editor and reporter.

Nothing has surprised me about the rise and shine of Donald Trump.

I saw it all before, 25 years ago — despite ugly behavior and demonstrated ignorance, people cheering for this combover bankruptcy acrobat to run for president.

The media get after him, but the media don’t have a clue about the back-brain, instinctual allure of this demigod of vulgarity. Just now, the media think they can shock us by exposing Trump as a man who cheats at golf, doesn’t know who Maj. Gen. Qasem Soleimani is and presides over companies that have gone through a lot of bankruptcies. Will they also hit him with those old campaign-trail gotcha questions — the price of a gallon of milk, a loaf of bread? A lot of voters, maybe most of them, don’t care.

Something more important is going on, some mystical fascination, a charisma. And he has always had it, or at least he had it a quarter-century ago on an April day when I learned everything I needed to know but little I could understand about Trump and the people of the United States.

The scene was the 1990 opening of his Trump Taj Mahal casino-hotel in Atlantic City, an opening he squeezed in just a year before the Taj went bankrupt. I was there for The Post, part of a medium-sized horde of reporters.

Bad times for The Donald, the way the media saw it. All the gossips agreed: He was broke. Spy magazine was calling him a “short-fingered vulgarian.” His brand was tacky, and his hair was weird.

And there he was, looking worried in the Taj lobby on opening day, his big face squinting and pouting amid the media he’d lured with promises of megawattage celebrities strobing around the place, except there weren’t any. It was as if the hero vulgarian of American literature, the Great Gatsby, had thrown a party and nobody came.

“Hey, Donald, where’s all the celebrities?”

“Wait and see, guys, you’ve never seen anything like this.”

“But where are they?”

He studied the lobby for a while.

“Hey!” he yelled. “You know who that is?”

He pointed to a woman checking in, big hat pulled down over big sunglasses, big raincoat collar turned up, a woman who clearly didn’t want to be seen here.

Did we know who that was? We looked and, as one, we yelled back: “Noooooooo!”

“That’s Elle Macpherson!” he said — yes, the Australian swimsuit model known as “The Body.” She scurried for the nearest elevator.

“How ’bout that?” Trump crowed. He was shameless.

He was also desperate. Time for leadership. He grabbed Jim Florio, the governor of New Jersey, and announced that we were going to take an impromptu tour of the casino. Like all casinos, it looked like a factory floor — all the people working away at slot machines, at least until Trump walked in and I saw the same Trump then as now, aglow with the attention, America opening its plutophilic heart to him despite, or more likely because of, all the preposterousness.

Instant panic. The state troopers shouted “Get back! Get back!” at the old women in sweaters who were going for him, shouting “Donald! Donald! Good luck!” in the toxic casino twilight. “Donald! Run for president!”

President! Who would think of Trump as president? Apparently a crazed crowd of New Jersey people, common people, bingo players, bus passengers, Mr. and Mrs. Front Porch USA — they thought he should be president of their United States of America.

“He’s number one, he’s a genius,” said Kathy Arena of Ramsey, N.J., who crouched with her camera while Trump glowed. “My husband, Tony, is pretty smart, too, but not that smart. Donald! Donald! I got to tell him, Tony! Donald, you’re more popular than the president!”

They even credited him with miracles.

New Jersey state Sen. Bill Gorman said: “I asked Donald Trump to meet with a disabled young man, and he said to that young man, ‘When the Taj opens, you’ll be there and you’re not going to be on crutches.’ He’s here tonight — and he’s not on crutches!”

A saint — by personifying in public the squalor we keep private, he redeems us.

The craziness grew. The crowd closed in.

“How do you get out of here?” he said. “Where’s the elevator?”

He was lost in his own casino. The troopers were lost, too.

He escaped, reaching for the door of a brown Cadillac limousine, though it turned out his car was the dark gray Lincoln.

“There goes a good man,” said Melvin Woolfolk, a retired Coast Guardsman. “I love him. He spends money. Most billionaires won’t spend a nickel, but he spends money. He’s gambling on this! He could lose! And I’m going to help him win!”

He waved a deck of credit cards. “I got my Visa, I got my Discovery, I’m gonna go in here and use ’em! I always lose. I’m 80 years old, why should I worry about my money? I don’t mind him taking it. There goes a beautiful man.”

And now, after all these years, by popular demand, he is the Republicans’ leading presidential candidate.