Donald's Trump has hit back at an author accusing him of having dementia by comparing himself to Ronald Reagan - the former president who suffered from Alzheimer's.
In his latest Twitter rant Trump likened himself to Reagan, saying the fellow Republican had the "same problem with fake news".
Trump vowed to be like the former actor as he attempts to weathers the storm caused by an explosive new book depicting him as unfit for office.
But the comparison has an implication that Trump may not have intended - as Reagan's own son believed he had suffered from the early signs of Alzheimer's while serving in the 1980s.
And now author Michel Wolff claims Trump's aides believe he could be showing the early signs of dementia.
Referring to "fake news", Reagan "handled it well" and "so will I", Trump wrote to his 46m followers after the book, "Fire and Fury", called into question Trump's mental capacity.
The billionaire has repeatedly used Twitter to defend himself from Wolff's that the president is unfit for office and his staff view him as a "child" and "semi-literate".
In his latest attack, Trump wrote on Sunday: "I’ve had to put up with the Fake News from the first day I announced that I would be running for President.
"Now I have to put up with a Fake Book, written by a totally discredited author.
"Ronald Reagan had the same problem and handled it well. So will I!"
Trump also made reference to Reagan in a series of tweets on Saturday in which he wrote that he's "like, really smart" and "a very stable genius".
Reagan had a combative relationship with the media, which had called his mental health into question at times.
He was diagnosed with Alzheimer's disease in 1994, five years after he left the White House, and died aged 93 in 2004. His son later claimed that he had shown symptoms of the disease while he was president.
Wolff claims Trump's aides believe he could have dementia, ADHD or learning difficulties, and fears over the president's mental capacity were widespread in the White House.
The author says Trump struggles to read "one page or one paragraph" of documents given to him, and he can't even follow a PowerPoint presentation.
The author depicted the White House as a "madhouse", saying Trump's "symptoms have got worse" since he assumed office in January last year.
Wolff told the Mail on Sunday that fears over the president's mental capacity were rooted in his childhood.
The author said: "He's just a rich wastrel. He was bad at school. They don't know if it's because he had learning disabilities.
"They discuss it at the White House: his apparent inability to read one page or one paragraph.
"He can't even follow a PowerPoint. They wonder where is that from. ADHD? A learning disability."
Wolff's book claims White House staffers believe Trump is "semi-literate" or even dyslexic as he barely reads.
He said: "Whether it's lack of sleep, the compounded effects of age... or there's actually some impairment - and that's a possibility - everybody around him discusses that."
The immediate bestseller claims the president barely reads, his comprehension of basic politics is limited, his attention span and focus are lacking, and he doesn't bother to listen to staff, instead relying on his own expertise.
Pitching policy to him is "like trying to figure out what a child wants", his deputy chief of staff Katie Walsh was quoted as saying.
The property tycoon told reporters that he had never granted Wolff an interview for the book and blamed former adviser Steve Bannon - who he called "Sloppy Steve" - for granting White House access.
But Wolff has insisted he interviewed Trump and members of his inner circle during on-the-record conversations, and he had recordings and notes to back up his claims.
Wolff's deeply critical account of Trump's first year in the White House was published ahead of schedule after excerpts set off a political firestorm.
Wolff alleges Trump didn't believe he would win the 2016 election, and was woefully unprepared when he assumed the role in January last year, lacking ideas and interest.
The journalist wrote: "Here, arguably, was the central issue of the Trump presidency, informing every aspect of Trumpian policy and leadership: He didn’t process information in any conventional sense.
"He didn’t read. He didn’t really even skim. Some believed that for all practical purposes he was no more than semi-literate.
"He trusted his own expertise - no matter how paltry or irrelevant - more than anyone else’s.
"He was often confident, but he was just as often paralyzed, less a savant than a figure of sputtering and dangerous insecurities, whose instinctive response was to lash out and behave as if his gut, however confused, was in fact in some clear and forceful way telling him what to do.
"It was, said Walsh, 'like trying to figure out what a child wants'.
Some staff members thought Trump was dyslexic, the explosive book claims.
Wolff also claims Trump has failed to recognise close friends and was prone to repeating comments.
The White House has since denied claims about Trump's mental health and Secretary of State Rex Tillerson has told CNN that he has never questioned the president's "mental fitness" and has no reason to.
Tillerson has reportedly called Trump a "moron" in the past.
Meanwhile, Wolff has suggested Trump could hold a grudge against the UK if he doesn't get an invite to Prince Harry and US actress Meghan Markle 's wedding this May.
Trump 'did not want to be president'
Michael Wolff's behind-the-scenes account of the White House is filled with juicy claims which have set off a political firestorm in Washington.
The bestseller claims Trump himself did not expect to be elected in November 2016 and he did not want to be president.
Wolff claims first lady Melania Trump was in tears of sadness on election night, and the couple rowed on inauguration day in January last year.
His book also claims that Trump's staff view him as a "child" and his and friends think he is incompetent, with media mogul and close friend Rupert Murdoch calling him a "f***ing" idiot after they discussed a visa scheme.
Trump gets bored during meetings with staff or foreign leaders - leaving some of them early - and struggles to understand basic politics, it was claimed.
Wolff also wrote that Trump and his wife sleep in separate bedrooms in the White House and barely speak, and that the president bragged about trying to bed his friends' wives.
It was claimed that Trump was unfaithful to the first lady and had very little to do with his children.
Wolff wrote that Trump is so afraid of being poisoned that he prefers to eat food from McDonald's because the staff don't know he is the customer.
Trump's daughter Ivanka allegedly mocked her dad's famous hairstyle and claimed he used Just for Men hair dye. Woff wrote: "She often described the mechanics behind it to friends: an absolutely clean pate - a contained island after scalp-reduction surgery - surrounded by a furry circle of hair around the sides and front, from which all ends are drawn up to meet in the center and then swept back and secured by a stiffening spray."
The president would resent being snubbed from the royal wedding and could torpedo Prime Minister Theresa May's hopes of a Brexit deal, Wolff warned.
He said that the billionaire has little regard for the UK's special relationship with the US and will only honour it if he "gets what he wants".
The author also warned that the president may try to "Trumpalise" the Queen and Buckingham Palace by viewing a State visit like a reality TV show.
It is unlikely that he will be on the guest list for the wedding of the year, as Harry is friends with former President Barack Obama and Meghan is a supporter of Trump challenger Hillary Clinton.
Wolff also said that Trump had no idea what Brexit was when he interviewed him two weeks before the 2016 referendum.
The US is the UK's largest single export market - behind the rest of the EU taken together - putting greater emphasis on a trade deal post-Brexit.