Updated at 1:07 p.m. ET

President Trump insisted Saturday that he is "a very stable genius," following the recent publication of a book that raises questions about his mental state and fitness for office.

Speaking to reporters at Camp David on Saturday, Trump called Michael Wolff, author of Fire and Fury: Inside The Trump White House,"a fraud" and reiterated his earlier claim on Twitter that Wolff is not trustworthy.

"So many of the people that I talk about in terms of fake news actually came to the defense of this great administration, and even myself, because they know the author, and they know he's a fraud," Trump told reporters, adding that he thinks the book is "a work of fiction."

In series of tweets on Saturday morning, Trump claimed that his ability to win the presidency on the first attempt shows he is mentally stable. Some partisans and political observers — primarily, though not exclusively, Democratsand liberals — along with some journalists have criticized Trump's psychological state, and last year, some prominent mental health professionals released armchair diagnoses of the president.

"Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart," Trump tweeted, noting: "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!"

Questions surrounding Trump's temperament intensified this week after excerpts from Fire and Fury detailed chaos inside the White House and portrayed an inept Trump at the helm.

Pulitzer-Prize-winning presidential historian Doris Kearns Goodwin tells Weekend Edition Saturday that Trump's "lack of humility" illustrates an issue with temperament.

"The ability to control impulses and emotions is a really important part of temperament of any leader, not just a president," she says. Trump knows "these tweets get him into trouble, and despite everyone saying, 'Stop,' he cannot stop."

But some on the right say Trump's tweets do not indicate he is mentally unstable.

"I think the president of the United States has shown he's very very capable; very, very talented," conservative commentator Ed Martin tells Weekend Edition. "He's a smart guy and he's in his right mind and he's doing a great job from where I sit for the country."

Although professional organizations disagree with the practice, some mental health professionals have publicly questioned Trump's mental state. Reports this week also revealed that a group of lawmakers from both sides of the aisle were briefed by Yale psychiatrist Dr. Bandy X. Lee about the president's fitness for office. Lee warned members of Congress in December that Trump "is unraveling" and "losing his grip on reality."

"We feel that the rush of tweeting is an indication of his falling apart under stress," Lee told Politico. "Trump is going to get worse and will become uncontainable with the pressures of the presidency."

Lee is the editor of The Dangerous Case of Donald Trump, written by 27 psychiatrists, psychologists and other mental health professionals, which offers analysis of Trump's psychological state. The book, and other armchair diagnoses of the president, has faced criticism because of policies by the American Psychological Association and the American Psychiatric Association that say it is unethical to psychoanalyze public figures from afar.

"Many of our greatest politicians have had psychiatric vulnerabilities," including Bill Clinton, Richard Nixon and Abraham Lincoln, says Ken Duckworth, a psychiatrist and medical director for the National Alliance on Mental Illness. He told NPR in December that these traits didn't necessarily make them incompetent or unfit for office.

Copyright 2021 NPR. To see more, visit https://www.npr.org.