Wolff tells The Hollywood Reporter the past few days have been very "surreal", and when asked if he's heard anything from White House sources, he said, "I hear that the president is very angry, or, let me be precise: I hear that he is truly bouncing off the walls".
"My credibility is being questioned by a man who has less credibility than, perhaps, anyone who has ever walked on earth at this point", Wolff said on NBC's "Today Show" Friday morning.
He later stated, "O$3 ne of the things we have to count on is that Donald Trump will attack, he will send lawyers' letters". "I am certainly and absolutely, in every way, comfortable with everything I've reported in this book".
Some people have expressed concerns the book is propaganda meant to slander the president, Phillips said, but he expects it to be one of their best sellers.
Michael Wolff made the claim in an interview with the BBC, responding Mr Trump's description of his book as "boring and untruthful". I never spoke to him for book.
That suit, brought by Summer Zervos, a former contestant on "The Apprentice", could force Trump to address sexual harassment claims against him.
Wolff's book has been heavily criticised by both Trump and Trump's supporters online, with the official GOP Twitter condemning the publication with its own satirical poster.
It has also sparked a public rift between Mr Trump and his former aide Steve Bannon, who is quoted as accusing Mr Trump's eldest son Donald Jr of "treasonous" behaviour in meeting a group of Russians.
Trump friend and ally Chris Ruddy, CEO of the right-wing Newsmax website, disputed on CNN that characterization, calling it "so absurd, so ridiculous".
White House press secretary Sarah Saunders said the book is "filled with false and misleading accounts" and is "trashy tabloid fiction". "They say he is a moron, an idiot", Wolff said.
About 250,000 copies of Fire and Fury have already been shipped.
Brad Phillips, assistant general manager, said they received more than 30 calls asking about the book the morning of its release. "He's like a pinball just shooting off the sides".
The election of Donald Trump was a shot heard around the world. The president said he never spoke to the writer - but Mr Wolff said the pair spent three hours together.
"Your publication of the false/baseless statements about Mr. Trump gives rise to, among other claims, defamation by libel, defamation by libel, defamation by libel per se, false light invasion of privacy, tortious interference with contractural relations, and inducement of breach contract", the letter says. Do you think he ever read that story?
He also spoke of how White House aides see the president as a "child" who needs "immediate gratification".
Wolff said the president was wrong. "Smart!" Trump tweeted about Rebekah Mercer and her family.