“Obviously, the hat provoked some of the stuff,” said Alexis Zimmerman, who was flying back to Newark from a business trip.

The man took an aisle seat three rows in front of her. She said he refused to let anyone sit beside him.

“He wanted to sit in the whole row by himself,” Zimmerman said.

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Her video shows him leaning back in his seat — hands folded behind his red hat, feet propped on someone else’s arm rest — while a woman in crutches and many others stand in the aisle, snap photos and glare.

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“This young lady’s not going to make it to her classes tomorrow and her tests she has to take, thanks to you,” a woman told the man. “Are you proud of yourself?”

“Guess what,” he replied. “In 45 minutes I’m going to collapse for not drinking my soda.”

The man said he was a diabetic, Zimmerman said. But at one point, passengers said, he also dared the flight crew to cuff him and drag him off the plane — reminding other passengers of last month’s infamous deplaning, amid a barrage of in-plane horror stories that have plagued United and the rest of the airline industry in recent years.

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But the United crew in Shanghai remained polite and patient throughout Sunday’s ordeal, said Clark Gredoña, another passenger.

“He was trying to explain to the crew and captain … because he had points, he felt he deserved an upgrade,” he said. “So this was his way of getting it.”

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But he got no upgrade. And before long, as seen in video, the man was waving his arms and shouting: “I have a seat here! … Shut up! … Moron!”

This went on for the better part of an hour, passengers Gredoña and Zimmerman said. And somehow in all of it, U.S. politics came up.

“I know people don’t like my hat,” Zimmerman heard the man say.

“He berated a female passenger,” Gredoña said. “I think he called her Hillary. Then he called her a lesbian. I think he called a stewardess ‘sweetheart.’ ”

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The man became “increasingly disruptive when asked to deplane,” a United spokesman said in a brief statement. “Local law enforcement was called to assist.”

Police had no more luck persuading him than anyone else. So Zimmerman, Gredoña and every other passenger had to return to the terminal and wait for the officers to remove him from the plane.

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Zimmerman said that took another two hours. Gredoña, who was partway home from a trip to the Philippines, had by then lost track of time.

He only knows a lot of it passed before the man finally emerged from the plane, escorted by police.

That’s when the whole incident took on a very electoral vibe. Cellphone video shows the man, still in his Trump hat, ascending an escalator — waving what appears to be a seat cushion at dozens of angry onlookers.

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Gredoña thinks the chanting started after the man taunted the crowd: “So I succeeded in making you guys waste three-and-a-half hours.”

People then shouted words unprintable.

And one shouted: “Lock him up!”

Then another, and another. “Lock him up, lock him up” — until a Chinese airport terminal sounded much like a latter-day Trump rally, when he and his crowds threatened his presidential campaign opponent, Hillary Clinton, with prison.

“I was one of those chanters,” Zimmerman said. “I didn’t start it. But oh my God, it was so funny, I couldn’t help myself.”

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The man remained defiant until the end — jeered in multiple languages, surrounded by police, he finally walked down the concourse and out of sight to an unknown fate.

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The plane would take off for the United States that evening, stopping for another delay in San Francisco so new crew could board, but eventually making it to Newark.

In the long and uneventful hours of the journey, passengers wondered who the man was — if he’d ended up in a Chinese jail, or if he’d been trying to provoke something with his political hat and escalating insults.