Donald Trump’s White House chief of staff secretly bought a book in which 27 mental health professionals warned that the president was psychologically unfit for the job, then used it as a guide in his attempts to cope with Trump’s irrational behavior.

News of John Kelly’s surreptitious purchase comes in a new book from Peter Baker of the New York Times and Susan Glasser of the New Yorker. The Divider: Trump in the White House, 2017-2021, will be published next week. The Guardian obtained a copy.

The book Kelly bought, The Dangerous Case of Donald Trump, was a bestseller in 2017. In January 2018 its editor, then Yale psychiatrist Bandy Lee, described its aims in a Guardian column.

She wrote: “While we keep within the letter of the Goldwater rule – which prohibits psychiatrists from diagnosing public figures without a personal examination and without consent – there is still a lot that mental health professionals can tell before the public reaches awareness.

“These come from observations of a person’s patterns of responses, of media appearances over time, and from reports of those close to him. Indeed, we know far more about Trump in this regard than many, if not most, of our patients.

“Nevertheless, the personal health of a public figure is her private affair – until, that is, it becomes a threat to public health.”

Kelly, a retired general, became Trump’s second chief of staff in July 2017 – after Trump fired Reince Priebus by tweet – and left the job in January 2019.

His struggles to impose order on Trump and his underlings and his virulent falling out with the president have been extensively documented. According to Baker and Glasser, who interviewed Kelly, the retired Marine Corps general bought a copy of The Dangerous Case of Donald Trump as he “sought help to understand the president’s particular psychoses and consulted it while he was running the White House, which he was known to refer to as ‘Crazytown’.”

“Kelly told others that the book was a helpful guide to a president he came to consider a pathological liar whose inflated ego was in fact the sign of a deeply insecure person.”

The authors report that Kelly’s view was shared by unnamed senior officials, quoting one as saying: “I think there’s something wrong with [Trump]. He doesn’t listen to anybody, and he feels like he shouldn’t. He just doesn’t care what other people say and think. I’ve never seen anything like it.”

The 25th amendment, which provides for the replacement of a president unable to meet the demands of the job, was seriously discussed at the end of Trump’s presidency, after the Capitol attack he incited.

Baker and Glasser say the amendment was tentatively discussed by cabinet members “within months of Trump taking office”. However, its flaws – if Trump opposed its use he would be all but impossible to shift – precluded further action.

Trump regularly dismissed claims about his mental health and his staff’s worries about it. In January 2018, after the publication of Michael Wolff’s tell-all book Fire and Fury, Trump memorably told reporters he was “a very stable genius”.

Kelly has regularly attacked Trump. In October 2020, CNN reported that Kelly told friends Trump’s dishonesty was “astounding … more pathetic than anything else” and called Trump “the most flawed person” he had ever met.

Trump blasted back, claiming Kelly “didn’t do a good job, had no temperament and ultimately he was petered out. He got eaten alive. He was unable to handle the pressure of this job.”

The Dangerous Case of Donald Trump was a bestseller, hailed by the Washington Post as “the most daring book” of 2017. But it also stoked controversy over its discussion of the mental state of a public figure.

In May 2020, Lee lost her job at Yale, in part, she said, over tweets about Trump. This month, a federal judge dismissed a lawsuit in which Lee said she was wrongfully fired.