'Art of the Deal' Ghostwriter: Trump is 'Deeply Disturbed' and 'Utterly Untrustworthy'

President Donald Trump speaks to the media at the White House before departing on Marine One on September 27. SAUL LOEB/AFP/Getty

The ghostwriter of President Donald Trump's best-selling book The Art of the Deal has suggested that the president may suffer from a personality disorder and said he is "deeply disturbed and utterly untrustworthy."

Tony Schwartz, who spent 18 months shadowing the businessman in the 1980s, offered his opinion on Trump's fitness for office ahead of the publication of a collection of essays by 27 psychiatrists and mental health experts assessing the president's psychological condition.

"The question that this book raises in a number of its essays by psychiatrists is: Is Trump crazy like a fox or is he just crazy?" said Schwartz, appearing on CNN's Anderson Cooper 360° on Thursday.

"And I think the overwhelming weight of evidence suggests that he's just crazy, and not crazy, casual crazy. I'm talking about crazy—I'm not a psychiatrist, so I actually can get away with saying this—but crazy as a personality disorder."

Related: Donald Trump will resign soon to save face, "The Art of the Deal" co-author predicted

The authors of the collection of essays—The Dangerous Case of Donald Trump—conclude that Trump is "the most dangerous man in the world" and that his role and behavior as president of the United States poses a threat to the safety and well-being of American citizens.

Schwartz also said that White House chief of staff John Kelly was man-managing Trump in a bid to limit the negative impact the president's actions might have.

"I do believe John Kelly knows clearly that Trump is deeply disturbed and that he is utterly untrustworthy, and he is managing him all the time out of some belief—put aside ideology—out of some belief that it's better that he be there than he not be there," said Schwartz.

"I never met anybody who worked for Trump who didn't know who Trump was within a very short time," he added.

Grace Mahoney, 16 months old, looks at a copy of "The Art of the Deal" before the start of an event with Republican presidential candidate Donald Trump in Portsmouth, New Hampshire, on October 15, 2016. MARY SCHWALM/AFP/Getty

The question of Trump's mental fitness arose on multiple occasions during the presidential campaign and continued during his first eight months in office. Psychiatrists are generally prohibited from commenting on the mental health of public figures without examining them, under so-called the Goldwater rule.

The principle was introduced by the American Psychiatric Association—the largest psychiatric group in the U.S. and the world—after a 1964 survey of psychiatrists in U.S. magazine Fact concluded that Republican presidential candidate Barry Goldwater was unfit for the office. Goldwater lost the 1964 election to Lyndon Johnson.

But there have been numerous examples of psychiatrists and mental health professionals bucking the rule after claiming they felt they had a duty to warn the public of the danger posed by Trump. In February, a letter signed by 35 mental health professionals and sent to The New York Times said that the "grave emotional instability indicated by Trump's speech and actions makes him incapable of serving safely as president."