President Donald Trump responded for the first time on camera Wednesday to journalist Bob Woodward’s explosive new book, "Fear: Trump in the White House," bashing it as a “work of fiction.”

“The book means nothing, it’s a work of fiction,” the president said to reporters brought into an Oval Office meeting with the Amir of Kuwait, noting that his secretary of defense and chief of staff have already issued statements rebutting their portrayal and purported comments in the book.

He also sought to discredit the reputation of Woodward, the famed Washington Post Watergate reporter, and asserted that the book becoming public was timed in order to interfere with the confirmation hearings of Supreme Court nominee Brett Kavanaugh.

“If you look back at Woodward’s past, he had the same problem with other presidents, he likes to get publicity, he sells some books,” the president said.

A short time later Wednesday, in a meeting with congressional leaders, Trump pushed back on a new Washington Post report that, even before Defense Secretary James Mattis was reported as saying in the Woodward book that Trump has the "understanding of "a fifth-or-sixth grader," the White House was actively discussing who would eventually replace him.

Trump praised Mattis and said he staying in his job.

"He'll stay right there, we're very happy with him, we're having victories people don't even know about," the president said when asked by a reporter, and thanked Mattis for the statement he made Tuesday refuting statements attributed to him in the Woodward book.

"He just made the nicest quote to me I think I've ever had ... the book is a total piece of fiction, he was not even misquoted, he didn't even make the statement," Trump said. "No I think he's a terrific person, he's doing a fantastic job as Secretary of Defense."

Even as Trump was trying to discredit Woodward, a key Republican ally on Capitol Hill, Sen. Lindsey Graham, called Woodward "a good reporter."

Earlier Wednesday, White House press secretary Sarah Sanders called the book "another repeat of pure fiction" fueled by interviews with disgruntled former employees. She disputed assertions, among other allegations, that President Trump called his attorney general Jeff Sessions "mentally retarded.”

"You can't have the type of success that this president has had if what that book says is true," Sanders said in an interview with ABC News chief anchor George Stephanopoulos on "Good Morning America" Wednesday, emphasizing the president's successes.

"Everything so far I've seen out of this book doesn't depict what's going on in the building behind me," Sanders said.

Woodward's previous reporting contributed to the downfall of the Nixon administration and he has written similar books about every president since.

The book, Woodward has said, is based on hundreds of hours of firsthand reporting and uses "deep background" sources -- people close to or in the White House who spoke anonymously.

Excerpts were released Tuesday and the full book is set for release Sept. 11.

"Look, he may have hundreds of hours of tapes but I think most of those probably come from disgruntled former employees,” Sanders told "Good Morning America" from Washington. “It's a lot of anonymous sources.”

Though Woodward says he tried to interview the president and went through about six people in the White House and Congress to do so, Trump called him only after his manuscript was complete. The president told Woodward he would've done an interview but wasn't aware of any requests. Woodward released audio of that phone conversation Tuesday.

"Look, I can't get into the internal deliberations," Sanders said of the decision not to do an interview with Woodward. "Obviously, the president would've wanted to. He knows he's his own best advocate.”

While Trump said he believed Woodward had "always been fair" in the phone conversation, he immediately went on the defense Tuesday and continued to criticize the book in a tweet after Sanders' interview on "Good Morning America" Wednesday.

Sanders responded to the president's tweet live on “Fox & Friends,” where she also did an interview Wednesday morning, by pivoting to his tax cut bill, the swift changes to the judiciary branch and acts of deregulation.

The White House plans to keep moving forward and "ticking off things on [Trump's] agenda," she told Fox News.

Her response mirrored the president's own comment in his phone call with Woodward. Trump told him he thought the book would be inaccurate, which Woodward denied.

"No, it's -- it’s going to be accurate, I promise," Woodward said.

"Well, accurate is that nobody’s ever done a better job than I’m doing as president," Trump responded.

Sanders made the same argument on "Good Morning America," touting the president's accomplishments.

"The things I see coming out of this White House are the president delivering on historic tax cuts, delivering on building a booming economy, delivering on rebuilding our military, delivering on remaking the judiciary, delivering on cutting regulation after regulation. What I see come out of this building is pure and total success," Sanders said. "He's had the most successful two years than any president in modern history and we're continuing to do that every single day."

In the book, Trump is described by staff as ignorant and impulsive. He's repeatedly painted as at odds with his closest officials, some of whom denied the book Tuesday.

Others, like former chief economic adviser Gary Cohn, who reportedly tried to leave after he was disappointed in the president's reaction to Charlottesville, Virginia, protests, former national security adviser General H.R. McMaster, whom Woodward said the president insulted by saying he dresses in cheap suits "like a beer salesman," or former senior White House adviser Steve Bannon, who reportedly called the president's daughter a "goddamn staffer," have yet to rebuke the book.

Secretary of Defense James Mattis and Chief of Staff John Kelly are among two of the officials who have denied the reporting. In statements, Kelly called the book "another pathetic attempt to smear people close to President Trump," while Mattis said the words attributed to him in the book were "never uttered by me or in my presence."

"You have people like General Mattis, General Kelly, two American heroes, come out and call the book pure fiction,” Sanders said Wednesday. “I would certainly rather take the word of those two individuals than a couple of disgruntled former employees that are anonymously attacking the president trying to make him look bad for no other reason I guess than to build themselves up.”

Stephanopoulos also asked Sarah about the president's tweet over the weekend that called attention to the investigations of two "popular" Republican congressmen facing serious corruption charges. The president complained about the potential loss of GOP seats and intimated that the DOJ should protect his allies in Congress.

Sanders said there's "often a double standard that takes place in the Department of Justice" but, when asked for specific details, did not say what that double standard is.

"Nobody disagrees with the fact if someone does something wrong it should be looked into," Sanders said. "The president wants that same type of fervor applied to some of the people that have been so politically biased against him and so politically biased against Republicans and conservatives to be looked at as well."

On Capitol Hill, Graham, while calling Woodward "a good reporter" sought to distance himself from a section in the book in which, according to a moment attributed to former White House chief strategist Steve Bannon, he sought to replace Senate Majority Leader Mitch McConnell, R-Ky.

Graham disputed that account Wednesday.

“I am very supportive of Senator McConnell, in the past and the present and the future,” Graham said. “I was working with Mr. Bannon about the Graham-Cassidy block grant [health care] proposal. He and Mitch McConnell had deep running disputes.”

He went on: “The idea I would replace Senator McConnell was mentioned and quickly disposed of. I said this is not about Mitch McConnell. It’s about getting a vote on a bill I thought was important for the country.”

“I have all the confidence in the world in Mitch. And I’ll tell you this, if anybody knows me. If I’ve got a problem with you, you’ll hear from me. You won’t read about it in a book.”

With regard to Trump, Graham told reporters, "The whole theme of the book is that President Trump can run hot and be volatile," adding he agrees.

Graham also explained to reporters that he tried to persuade Trump to sit down with Woodward to be interviewed for the book during one of their many golf outings. He referred to their conversation as a “brief intervention.”

“I always believe it's better to sit down and tell your story, but it was a brief intervention on the golf course and it went like this: 'Mr. President, I think Woodward is writing a book about your presidency. He does it about every president, I'm sure he would like to talk to you, you might want to think about that.' And that was it,” Graham said.

ABC News' Meridith McGraw, Mariam Khan and Benjamin Siegel contributed to this report.