Washington(CNN) President Donald Trump slammed reports questioning his mental stability in a series of tweets Saturday morning, writing he's a "very stable genius" after the publication of an exposé about his first year as President put the White House into damage-control mode.

"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 ... " Trump wrote, referring to questions raised about the mental fitness of the former President, who disclosed in 1994 that he had Alzheimer's disease.

"Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart," the President continued. "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!"

After his tweets Saturday morning, Trump told reporters at Camp David that Wolff is a "fraud" who doesn't know him.

"I went to the best colleges, or college," he told reporters. "I had a situation where I was a very excellent student, came out and made billions and billions of dollars, became one of the top business people, went to television and for 10 years was a tremendous success, as you probably have heard, ran for President one time and won. Then I hear this guy that doesn't know me at all, by the way, didn't interview me, said he interviewed me for three hours in the White House. Didn't exist, it's in his imagination."

Trump continued: "I never interviewed with him in the White House at all; he was never in the Oval Office."

Wolff told "Today" show host Savannah Guthrie on Friday that he "absolutely spoke to the President" while working on "Fire and Fury."

"Whether he realized it was an interview or not, I don't know, but it certainly was not off the record," Wolff said. "I've spent about three hours with the President over the course of the campaign, and in the White House. So, my window into Donald Trump is pretty significant."

The remarkable spectacle of Trump defending his mental stability comes after the President and some of his top officials spent the last few days countering claims in author Michael Wolff's new book, "Fire and Fury," about Trump's mental fitness to serve as President. The book, which went on sale Friday, also paints the picture of a President who neither knows nor cares about policy and doesn't seem to perceive the vast responsibilities of his role.

CNN has not independently confirmed all of Wolff's assertions.

Trump's tweets also come after reports surfaced that a dozen lawmakers from the House and Senate received a briefing from Yale psychiatrist Dr. Bandy X. Lee on Capitol Hill in early December about Trump's fitness to be president.

"Lawmakers were saying they have been very concerned about this, the President's dangerousness, the dangers that his mental instability poses on the nation," Lee told CNN in a phone interview Thursday, "They know the concern is universal among Democrats, but it really depends on Republicans, they said. Some knew of Republicans that were concerned, maybe equally concerned, but whether they would act on those concerns was their worry."

The briefing was previously reported by Politico. Lee, confirming the December 5 and 6 meeting to CNN, said that the group was evenly mixed, with House and Senate lawmakers, and included at least one Republican -- a senator, whom she would not name.

Lee's public comments are highly unusual given protocols from medical professional organizations -- including the 37,000-member American Psychiatric Association -- banning psychiatrists from diagnosing patients without a formal examination.

The White House has taken issue with the claims in Wolff's book since excerpts of it began to surface online ahead of its publication, with press secretary Sarah Sanders calling it "complete fantasy" and an attorney for Trump sending a "cease and desist" threat to the book's author and publisher.

Trump issued a scathing statement on his former chief strategist, Steve Bannon, saying he had "lost his mind" after the book quoted Bannon making negative remarks about Trump and son Donald Trump Jr.

The book quoted Bannon as calling a June 2016 meeting between a Russian lawyer and the President's eldest son, son-in-law Jared Kushner and then-campaign chairman Paul Manafort "treasonous" and "unpatriotic."

Bannon also reportedly told Wolff: "They're going to crack Don Junior like an egg on national TV."

Trump lit into Bannon in a tweet Friday night, saying he "cried when he got fired and begged for his job."

"Michael Wolff is a total loser who made up stories in order to sell this really boring and untruthful book," Trump wrote. "He used Sloppy Steve Bannon, who cried when he got fired and begged for his job. Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad!"

Wolff reiterated his belief that it is becoming a widespread view that Trump is unfit for presidency, telling BBC Radio in an interview overnight that it's a "very clear emperor-has-no-clothes effect."

"The story that I have told seems to present this presidency in such a way that it says he can't do his job," Wolff said in the interview. "Suddenly everywhere people are going, 'Oh my God, it's true, he has no clothes.' That's the background to the perception and the understanding that will finally end ... this presidency."

Secretary of State Rex Tillerson told CNN in an exclusive interview on Friday he's never questioned Trump's mental fitness, despite reports he once called Trump a "moron."

"I've never questioned his mental fitness," Tillerson told CNN's Elise Labott. "I have no reason to question his mental fitness."