IT'S NOT A COMPLEX IF YOU ARE INFERIOR:

The two most influential role models in Mr. Trump's youth were men who preached the twin philosophies of relentless self-promotion and the waging of total war against anyone perceived as a threat.

Mr. Trump, according to one longtime adviser, is perpetually playing a soundtrack in his head consisting of advice from his father, Fred, a hard-driving real estate developer who laid the weight of the family's success on his son's shoulders. Mr. Trump's other mentor was the caustic and conniving McCarthy-era lawyer Roy Cohn, who counseled Mr. Trump never to give in or concede error.

Mr. Trump's fixation on Mr. Obama and an F.B.I. investigation into Russian influence in the 2016 election echo his actions in New York decades ago, when he engaged in bitter personal battles with the mayor, Edward I. Koch, and the city fathers of Atlantic City. The battles were often to the detriment of Mr. Trump's real estate and gambling businesses, according to Tim O'Brien, author of "TrumpNation," a 2005 biography that documented his early years.

"I don't think there's anything new here in his behavior,'' said Mr. O'Brien, now the executive editor of Bloomberg View. "He's been doing this kind of thing for the last 45 years.''

"He's deeply, deeply insecure about how he's perceived in the world, about whether or not he's competent and deserves what he's gotten," he added. "There's an unquenchable thirst for validation and love. That's why he can never stay quiet, even when it would be wise strategically or emotionally to hold back."

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