He was also a skilled negotiator with an almost supernatural ability to pinpoint and attack his adversaries’ vulnerabilities, as several of his Republican primary opponents discovered. Since his financial emergency in the 1990s, he appears to have sworn off taking on large amounts of debt, and instead has used his brand to collect fees on real estate and other projects. This has greatly limited his downside risk, but has also capped the amount he can earn, since he often does not own the underlying equity on the projects that bear his name.

Since leaving journalism in 1993, I have been a Wall Street real estate analyst and a hedge fund manager. I have studied how businesses thrive and why they fail. Mr. Trump’s political rise has been maddening for me to watch, and I sometimes feel like the character played by Kevin Bacon in the movie “Diner” who screams the right answers to a TV quiz show as the contestants get them wrong.

“The issue isn’t that he’s crass,” I want to shout. “It’s that he’s a bad businessman!”

Hanging on my office wall is a letter written on gold-leaf stationery, dated March 22, 1990. “Dear Neil,” it reads. “From your first incorrect story on Merv Griffin — to your present Wall Street Journal article, you are a disgrace to your profession! Sincerely, Donald J. Trump.” (Mr. Griffin was a Trump rival.)

The article I had just written took a skeptical look at the ability of Mr. Trump’s newly opened Trump Taj Mahal Atlantic City casino to make the interest payments on its bonds. I quoted an analyst saying, “Once the cold winds blow from October to February, it won’t make it.” Mr. Trump complained to the man’s employer. Within days, the analyst was fired. But his prediction would prove prescient.

At 70, Mr. Trump is 12 years older than I am. As I watched his career soar in the 1980s and the inordinate amount of press attention he attracted, I was struck by two things: His list of real estate accomplishments were minuscule compared with those of more successful New York developers who garnered far less publicity, and he lied a lot. He made up the prices he was getting for his condominiums, the value of bids he had turned down for various properties and his prospects for luring corporate tenants to his buildings.

And, of course, he lied about his wealth.

Then and now, we in the media helped enable the Trump myth. He made great copy. Early on, I noticed that any article I wrote about him — whether for the tabloid Daily News or the serious Wall Street Journal — would get great play. This invariably led me and others to dig deeper for Trump news.

Oddly, he seemed less interested in making money than in creating the perception that he was wealthy. This is why, I believe, he continually floated plans to build the world’s tallest building. People would notice. His feuds with Forbes magazine over his net worth were legion.