As the ghostwriter for Donald Trump’s 1987 memoir The Art of the Deal, Tony Schwartz spent more than a year with the businessman. The book, which was largely penned by Schwartz, helped create Trump’s national reputation as a savvy dealmaker.

For the next 30 years, Schwartz watched as Trump’s fame continued to grow — first as the star of the reality show The Apprentice, and eventually as the presumptive nominee for the Republican Party.

While he was working on the book, Trump gave Schwartz unprecedented access to his business dealings, letting him listen in on dozens of calls. As a result, Schwartz says, he got to know Trump better than anyone outside his family. In a new interview with the New Yorker, Schwartz says he "genuinely" believes that if Trump were the president of the United States, "there is an excellent possibility it will lead to the end of civilization":

"I put lipstick on a pig," he said. "I feel a deep sense of remorse that I contributed to presenting Trump in a way that brought him wider attention and made him more appealing than he is." He went on, "I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilization." If he were writing "The Art of the Deal" today, Schwartz said, it would be a very different book with a very different title. Asked what he would call it, he answered, "The Sociopath."

This, of course, is strikingly different from the narrative Trump has told on the campaign trail.

Trump has built his presidential campaign as a bombastic and foolhardy candidate, but he has long hinted that he’ll be able to change his stripes once he gets to the Oval Office. "I can be the most politically correct person you have ever seen," he said at an Iowa rally in January. "When I’m president I’m a different person."

But Schwartz portrays Trump as a pathologically self-centered man with the attention span of a 9-year-old. Given that the president is often called on to quickly absorb complex information and then make high-stakes decisions, this personality trait might prove to be a liability in the White House.

Watch: The political science that predicted Trump's rise