- Video report by ITV News Washington Correspondent Robert Moore
Donald Trump has doubled down on his attacks against the author of a new book about his presidency, labelling him a "fraud" and calling the book "fiction".
Mr Trump attacked Fire and Fury author Michael Wolff when speaking to reporters from Camp David, the presidential retreat in Maryland, ahead a meeting with Republican leaders.
The book claimed Oval Office staff believed the 45th president was not mentally fit to hold office.
"I consider it a work of fiction," Mr Trump said, before bemoaning what he called the country's "weak libel laws" and taking a swipe at former chief strategist Steve Bannon, who was one of the main sources of the book.
"I don't know this man - I guess sloppy Steve brought him in the White House quite a bit and it was one of those things.
"That's why sloppy Steve is now looking for a job."
Earlier on Saturday he dismissed allegations he is unfit to be president, proclaiming himself to be a "very stable genius" in a series of tweets.
Mr Trump said two of his "greatest assets have been mental stability and being, like, really smart".
In his latest online onslaught, Mr Trump accused his critics of trying to make an issue of his "mental stability and intelligence".
"Now that Russian collusion, after one year of intense study, has proven to be a total hoax on the American public, the Democrats and their lapdogs, the Fake News Mainstream Media, are taking out the old Ronald Reagan playbook and screaming mental stability and intelligence," he wrote in a series of trademark tweets.
"Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart. Crooked Hillary Clinton also played these cards very hard and, as everyone knows, went down in flames. I went from VERY successful businessman, to top T.V. Star to President of the United States (on my first try). I think that would qualify as not smart, but genius....and a very stable genius at that!"
Responding to claims in the Wolff's book, Fire and Fury: Inside The Trump White House that the president has a short attention span, regularly repeats himself and refuses to read briefing notes, secretary of state Rex Tillerson told CNN that he had "no reason to question his mental fitness."
But despite defending Mr Trump, Washington's chief diplomat admitted the president has a very different decision making process and Mr Tillerson has spent a lot of time "understanding how to best communicate with him."