The anonymous staff member questions Mr Trump’s fitness for office in a book published later this month under the title A Warning.
“I am not qualified to diagnose the president’s mental acuity,” the author writes, according to a review by The Washington Post. “All I can tell you is that normal people who spend any time with Donald Trump are uncomfortable by what they witness.
“He stumbles, slurs, gets confused, is easily irritated, and has trouble synthesising information, not occasionally but with regularity.
“Those who would claim otherwise are lying to themselves or to the country.”
The 259-page book is a follow-up to an opinion piece published in The New York Times last year, in which the author claimed to “part of the resistance inside the Trump administration”.
Mr Trump is described variously as “a twelve-year-old in an air traffic control tower” and an “elderly uncle running pantsless across the courtyard” of a nursing home while “cursing loudly about the cafeteria food, as worried attendants tried to catch him”.
“You’re stunned, amused, and embarrassed all at the same time,” the author adds.
The anonymous official admits he sat in “uncomfortable silence” as the president made offensive jokes about a woman’s appearance or performance.
“He comments on makeup, he makes jokes about weight,” the author writes. “He questions the toughness of women in and around his orbit. He uses words like ‘sweetie’ and ‘honey’ to address accomplished professionals.
“This is precisely the way a boss shouldn’t act in the work environment.”
The anonymous official says that “the last straw” which prompted his decision to speak out was the president’s attempt to prevent the White House flag being lowered to half-mast after the death of senator John McCain.
However the author opposes removing the president from office through impeachment proceedings or by using the 25th amendment, arguing that his would cause “further disunion”. He instead hopes that Mr Trump is not re-elected.
The author also admits that his description of a White House resistance movement was overblown, adding: “Unelected bureaucrats and cabinet appointees were never going to steer Donald Trump the right direction in the long run, or refine his malignant management style. He is who he is.”
On Monday, the Justice Department sent a letter to the book’s publisher and the writer’s literary agency, suggesting a confidentiality agreement may have been violated and asking for information that could help reveal the author’s identity.
The publisher, Hachette, responded by saying it would provide no additional information beyond calling the author a “current or former senior official”.
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