Perhaps the best way to understand Donald Trump is as a case of arrested development.

In terms of personality and worldview, Trump is stuck in middle school. Early middle school.

And that’s being charitable.

Part of growing up is developing self-control. Trump never has. Listen to him in the presidential debate, interjecting compulsively, and flash back to seventh grade and the boy in the back of the class who kept interrupting the teacher with wisecracks. It was amusing the first time or two. Then it became annoying.

We grew so inured to Trump’s antics during the primary campaign that there is a risk of forgetting how great a departure his mugging for the camera and interrupting opponents is from the rather staid norm, especially during general-election debates. Trump interrupted Hillary Clinton and moderator Lester Holt a whopping 55 times . “Not,” Trump said. “Wrong.” “Facts.” “Take a look at mine.”

In the wake of this first round of presidential debates, The Washington Post opinions section brings you Republican presidential nominee Donald Trump’s (not so) presidential look. (Adriana Usero/The Washington Post)

But Trump the interrupter is not the only manifestation of Schoolboy Trump. Part of growing up is learning to take responsibility for your mistakes, and to accept criticism. Trump never has. Nothing that goes wrong is ever his fault. It’s always the malfunctioning microphone (and who was behind that?) or the hostile moderator (who did a good job, Trump pronounced, before his own bad reviews came in).

Part of growing up is learning to manage your temper. Trump never has. He can be baited, as Clinton says, with a tweet. If criticized — in Trump’s perception, if attacked, because all criticism is hostile and nasty and intolerable — he has to fight back. There is no alternative. If critics go low, he goes lower. See Friday’s tweet-storm on former Miss Universe Alicia Machado.

And part of growing up is learning to treat others decently, even if you have the power to do otherwise. Trump never has. During the 2012 campaign, reporters unearthed the incident of high school Mitt Romney and a gang of followers assaulting and clipping the hair of a student whose long locks (and apparent homosexuality) offended their sensibilities. The story rattled but didn’t stick — because grown-up Romney evolved into a better version of his prep-school self.

Trump hasn’t. Neighbors recall him at 5 or 6, hurling rocks across the fence at a playpen — with an infant inside. Slightly older Trump pulled pigtails; punched, by his own description, a second-grade teacher; led his crew in beating up a neighborhood boy.

The childhood bully is father of the man. The adult rock-thrower hurls insults — “Miss Piggy,” “Miss Housekeeping” — and humiliates with public displays of power over subordinates. “The temperament is not that different,” Trump once told a biographer, in a rare moment of self-knowledge.

But if Trump is trapped in middle school, he is also preserved in the amber of his particular historical moment. His worldview is fossilized, in part, in the late 1950s — pre-civil rights, pre-women’s lib. Thus Trump can explain, with all apparent sincerity, that, as proof that “there’s nobody that’s done so much for equality as I have,” he is to be congratulated for opening a private club that did not discriminate against African Americans. In 1995.

“In Palm Beach, Florida, tough community . . . I opened a club, and really got great credit for it,” Trump said at the debate. “No discrimination against African Americans, against Muslims, against anybody. . . . And I have been given great credit for what I did.”

And then there is Trump’s “Mad Men”-era vision of male-female roles. In Trump world, real men don’t change diapers. “There’s a lot of women out there that demand that the husband act like the wife and you know there’s a lot of husbands that listen to that,” Trump said on radio’s “Opie and Anthony Show” in 2005. “I’m really like a great father, but certain things you do and certain things you don’t.” Like push strollers. “I’ll supply funds and she’ll take care of the kids. It’s not like I’m gonna be walking the kids down Central Park,” he told Howard Stern that same year.

And women, of course, matter primarily for their looks. “Look at that face! Would anyone vote for that?” Trump said of primary rival Carly Fiorina . His subsequent backpedaling reinforced the retro point: Fiorina, Trump acknowledged, was “a beautiful woman” after all.

Many people recall middle school as a miserable experience. Even more miserable: a middle-schooler in the Oval Office.

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