Veteran journalist Bob Woodward said Monday in an exclusive interview on NBC News' "Today" that President Donald Trump is "detached" from reality and jeopardizes American national security.

"I've never seen an instance when the president is so detached from the reality of what's going on," Woodward said.

Trump responded within an hour, calling the author a "liar" and a political "operative" for Democrats.

In his first live TV interview for the book's release, the Washington Post editor and author of "Fear: Trump in the White House" recounted an incident in which the president complained about U.S. troops in the Korean peninsula. Woodward said the president's staff tried to explain that this is a defensive measure.

"James Mattis says we're doing this to prevent World War III," Woodward added. "The idea that the secretary of defense has to tell a president that all of these actions are designed to prevent the ultimate catastrophe. And Mattis goes on and says if we don't keep these programs, which are very sensitive, the only deterrent program we have will be the nuclear option."

Woodward depicts widespread White House dysfunction in "Fear," raising explosive allegations of a paranoid president whose own staff believes is unhinged and erratic. The book's findings were amplified when The New York Times published an anonymous op-ed from a senior administration official, claiming the president's staff seeks to thwart his "more misguided impulses." The book will be released on Tuesday.

"This has not been treated seriously enough," Woodward said on "Today." "The things — some of the things — that Trump did and does jeopardizes the real national security."

The president tweeted before and after the interview on Monday, attacking Woodward and the book.

"I'll write the real book!" Trump wrote before the interview.

"Bob Woodward is a liar who is like a Dem operative prior to the Midterms. He was caught cold, even by NBC," he wrote in a tweet after the interview.

“It is mostly anonymous sources in here, why should anyone trust you? General Mattis, General Kelly said it’s not true.” @SavannahGuthrie @TODAYshow Bob Woodward is a liar who is like a Dem operative prior to the Midterms. He was caught cold, even by NBC. — Donald J. Trump (@realDonaldTrump) September 10, 2018

On "Today," Woodward pushed back on criticism that his book relies entirely on unnamed sources and the White House insiders and others who have claimed his reporting is inaccurate.

"The incidents are not anonymous. It gives a date, it gives a time, who participates, most often the president himself and what he says," Woodward said.

Asked if the Trump showed signs of mental defect, Woodward said that "my job here is not to psychoanalyze, it's to describe what happened. On specific dates, in specific moments."

His interviews for the book, Woodward added at the close of his "Today" interview, were recorded.