United States President Donald Trump on Saturday rejected doubts about his mental health that were mentioned in a new book on his presidency, and said that the author, Michael Wolff, was a “fraud” and had penned a work of fiction.

The president, who called himself a “stable genius”, accused the Democratic Party and the media of questioning his mental stability in order to discredit him. “Actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart,” Trump tweeted.

The book, Fire and Fury: Inside the Trump White House, was scheduled for release on January 9, but its description of how Trump runs the government and allegations that the president was unprepared for his job stirred controversy and increased interest in the book.

After Trump’s lawyer said he would try to stop the book from being published, publisher Henry Holt & Co advanced the book’s release to Friday midnight.

The president said that the media had adopted the “Ronald Reagan playbook”. The 40th American president’s second term was dogged with speculation about his mental health. Reagan in 1994 announced that he had Alzheimer’s, five years after leaving office.

The book quotes some of the president’s closest advisors, who questioned his fitness to lead the country.

“I went to the best colleges, 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,” he told reporters at Camp David after meeting senior leaders of the Republican Party to decide the legislative agenda for the year.

The book portrays Trump as an impatient man struggling to understand policy issues BBC reported. He often often rambles and repeats himself, Wolff reportedly says.