WASHINGTON (AP) - President Donald Trump, portrayed in a new book as a leader who doesn't understand the weight of his office, took to Twitter on Saturday to defend his mental fitness and boast about his intelligence, saying he is "like, really smart" and "a very stable genius."

He posted a series of tweets from Camp David, the presidential retreat in Maryland, a few hours before holding meetings on the 2018 legislative agenda with Republican congressional leaders and Cabinet members.

It was his latest pushback against author Michael Wolff's "Fire and Fury: Inside the Trump White House." The book draws a derogatory portrait of the 45th president as an undisciplined man-child who didn't actually want to win the White House, and who spends his evenings eating cheeseburgers in bed, watching television and talking on the telephone to old friends.

The book also quotes Trump's former chief strategist, Steve Bannon, and other prominent advisers as questioning the president's competence.

Trump is having none of it.

He tweeted that critics are "taking out the old Ronald Reagan playbook and screaming mental stability and intelligence." The president said "actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart."

Trump said going from successful businessman to reality TV star to president on his first try "would qualify as not smart, but genius .... and a very stable genius at that!"

Reagan died in 2004, at age 93, from pneumonia complicated by the Alzheimer's disease that had progressively clouded his mind. At times when he was president, Reagan seemed forgetful and would lose his train of thought while talking.

Doctors, however, said Alzheimer's was not to blame, noting the disease was diagnosed years after he left office. Reagan announced his diagnosis in a letter to the American people in 1994, more than five years after leaving the White House.

Trump, now 71, was the oldest president ever when assuming office. Reagan was nearly eight months younger.

Chatter about Trump's mental fitness for office has intensified in recent months on cable news shows and among Democrats in Congress.

White House spokeswoman Sarah Huckabee Sanders this week called such suggestions "disgraceful and laughable."

"If he was unfit, he probably wouldn't be sitting there and wouldn't have defeated the most qualified group of candidates the Republican Party has ever seen," she said, calling him "an incredibly strong and good leader."

In early December, the House voted overwhelmingly to kill a resolution from a liberal Democrat to impeach Trump. Rep. Al Green, D-Texas, said Trump had associated his presidency with causes rooted in bigotry and racism.

To back his claim accusing Trump of high misdemeanors, Green cited incidents such as Trump's blaming both sides for violence at a deadly white supremacist rally in Charlottesville, Virginia, and his sharing of hateful, anti-Muslim videos posted online by a fringe British extremist group.

House Minority Leader Nancy Pelosi, D-Calif., and Minority Whip Steny Hoyer, D-Md., said in a statement shortly before the vote that while "legitimate questions have been raised about his fitness to lead this nation," they argued "now is not the time to consider articles of impeachment."