Donald Trump refuted reports that he is not mentally fit for office. Getty

Journalist Michael Wolff's new bombshell book, "Fire and Fury: Inside the Trump White House," has asserted that many in President Donald Trump's inner circle have questioned his mental fitness, prompting a firm rebuke by the president over the weekend.

According to Wolff, aides believe he may have dementia or learning difficulties. In an interview Friday on NBC's "Today," host Savannah Guthrie pressed Wolff on whether every person surrounding Trump, including senior advisers and family members, have questioned his intelligence and fitness for office.

"Let me put a marker in the sand here: 100 percent of the people around him," Wolff said.

Wolff added that Trump's eldest daughter, Ivanka Trump and her husband, Jared Kushner, who also serves as a White House senior adviser, have placed blame on the president for the couple's legal quagmire.

"There was now a fair amount of back-of-the-classroom giggling about who had called Trump what. For Steve Mnuchin and Reince Priebus, he was an 'idiot.' For Gary Cohn, he was 'dumb as s---.' For H.R. McMaster he was a 'dope.' The list went on," according to the book.

“The one description that everyone gave, everyone has in common — they all say 'he is like a child.' And what they mean by that he has a need for immediate gratification. It’s all about him," Wolff said.

Wolff says his book has included more than 200 interviews, many of which were taped. Trump has made efforts to discredit "Fire and Fury," claiming that Wolff had "zero access to the White House" and that he "never spoke to Wolff." In Twitter postings Saturday, while Trump has huddled with Republican lawmakers at Camp David, Trump described himself as a "genius."

On Sunday, Trump again attacked Wolff and his assertions, invoking former President Ronald Reagan, who battled questions about dementia in the final years of his eight-year term.

Questions surrounding Trump's mental fitness are not new. In an August appearance on CNN's "State of the Union," Rep. Adam Schiff, D-Calif., said he and his colleagues had grown increasingly concerned about Trump's mental health.

“There are some serious issues,” Schiff said, and added that “the pressures of the job may only get worse.”

U.S. Ambassador to the United Nations Nikki Haley on Sunday defended Trump administration staffers on ABC's "This Week with George Stephanopoulos.”

"These people love their country and respect our president. I've never seen or heard the type of toxic language that they are talking about ... No one questions the stability of the president,” Haley said.