There is never any question about authorship: Mr. Trump’s style of writing sounds virtually identical to his hyperbolic manner of speech, with a healthy sprinkling of the words “great” and “tremendous,” abundant displays of self-regard and over-the-top claims of success or doom.

In a 1985 letter to Mayor Edward I. Koch, Mr. Trump predicted New York City’s imminent downfall if a fellow real estate developer, Arthur E. Imperatore Sr., were allowed to start a ferry service between New Jersey and Manhattan. “Real estate values and taxes in New York would plummet,” Mr. Trump prognosticated darkly. “Why would anyone want to live or shop in New York?” (Mr. Imperatore started the ferry service without destroying New York’s economy.)

As a writer, Mr. Trump sometimes reached, awkwardly but earnestly, for eloquence. In a 1983 letter to A. M. Rosenthal, then the executive editor of The Times and a lunch companion, Mr. Trump turned poetic as he tried to capture his reaction to an article that Mr. Rosenthal had written about returning to Poland for the first time in decades.

Image Charlie Sykes, a conservative radio talk show host who has opposed Mr. Trump, received a note from him scrawled next to an article on the front page of The New York Times about skeptical Republicans warming to Mr. Trump. Credit... via Charlie Sykes

“It is moving; it is sad; it is hopeful (?); it is devastating,” Mr. Trump wrote, saying that his wife at the time, Ivana, who grew up in Eastern Europe, agreed. “It truly captured the strength, the will and the soul of the Polish people,” Mr. Trump wrote.

He could write with striking tenderness to Ivana, according to notes reviewed by The Times. “I adore and love my little darling,” he wrote to her in one. “I truly believe that you are the greatest,” he wrote in another.

On the page, anyway, Mr. Trump was even capable of humility, describing himself as a scribe of “little talent” in a 1985 note to Arthur Ochs Sulzberger, then the publisher of The Times. (Mr. Trump had an agenda: to complain about a reporter he disliked.)