Among the many claims included is the shock allegation that advisers swiped documents off the Oval Office desk to stop him signing them.
The book says the US President’s former economic adviser, Gary Cohn, removed a letter about a trade agreement with South Korea because he thought it was a threat to national security.
Defence Secretary James Mattis is said to have once claimed that Mr Trump had the intelligence of a “ fifth grader” after the President reportedly told him to assassinate Syrian President Bashar al-Assad with the order: “Let’s ******* kill him!”
Chief of staff John Kelly also thinks that Mr Trump is an “idiot” and said his presidency was in “crazy town”, according to the book.
The jaw-dropping claims all feature in Fear: Trump In The White House written by Bob Woodward, one of the reporters who exposed the Watergate scandal in the 1970s.
The book is out on Tuesday, but extracts were published by the Washington Post yesterday.
Unlike previous books about the Trump White House, Mr Wood- ward’s work was extensively researched with dozens of tape interviews with sources, making it harder for the President to dispute the claims.
Mr Woodward writes that Mr Trump was presiding over “a nervous breakdown of the executive power of the most powerful country in the world”.
His inner circle tried to restrain his impulses and stop damaging information from reaching him.
According to the book, Mr Cohn “stole a letter off Trump’s desk” that the President was intending to sign to formally withdraw the US from a trade agreement with South Korea.
Mr Cohn later claimed that Mr Trump did not even notice that it was missing.
When another aide drew up an order to withdraw the US from the North American Free Trade Agreement with Mexico and Canada, Mr Cohn reportedly said: “I can stop this. I’ll just take the paper off his desk.”
Mr Trump’s knowledge of foreign affairs left Mr Mattis thinking that his boss had the intelligence level of an 11-year-old, the book says.
Mr Woodward writes that the President was dismissive about having the US military on the Korean peninsula, even though it allowed them to detect a North Korean missile launch in seven seconds rather than 15 minutes from Alaska. Mr Mattis explained troops were there “in order to prevent World War III”.
Mr Woodward also writes that after Bashar al-Assad launched a chemical attack on Syrian civilians in April 2017, Mr Trump called Mr Mattis and said he wanted him dead.
The President allegedly shouted: “Let’s ******* kill him!
“Let’s go in. Let’s kill the ******* lot of them.” Mr Mattis is said to have hung up the phone and told a senior aide: “We’re not going to do any of that.”
Mr Trump later authorised a conventional air strike on Syria.
At one point Mr Kelly, the chief of staff, reportedly said of Mr Trump during a staff meeting: “He’s an idiot. It’s pointless to try to convince him of anything. He’s gone off the rails.
We’re in crazy town. I don’t even know why any of us are here. This is the worst job I’ve ever had.”
Mr Trump is also said to have mocked Attorney General Jeff Sessions’s accent and allegedly described him to a staffer as “mentally retarded… he’s this dumb Southerner”.
The President is also said to have lashed out at former New York mayor Rudy Giuliani, now his attorney, and reportedly said he was a “baby” after he appeared on TV to defend Mr Trump over harassment allegations.
Mr Trump allegedly said: “I’ve never seen a worse defence of me in my life. They took your diaper off right there. You’re like a little baby that needed to be changed. When are you going to be a man?