President Trump ratcheted up his criticism of veteran reporter and author Bob Woodward, calling his new book a "joke."

Woodward spoke to NBC's "Today" show Monday morning, a day before the release of "Fear," warning that Trump is "detached from the reality of what's going on" and arguing there could be national security consequences. 

Trump blasted back at Woodward on Twitter in a series of tweets, calling the book a "scam" and a "joke" and accusing Woodward of lying and making up quotes.

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In the book, Woodward claims Defense Secretary James Mattis once said Trump has the understanding of "a fifth- or sixth-grader" and that White House Chief of Staff John Kelly called Trump an "idiot."

Mattis and Kelly have both denied the quotes attributed to them. 

Woodward said his book does not rely on anonymous sources, telling Savannah Guthrie, "The incidents are not anonymous. It gives a date, it gives a time, who participates, most often the president himself and what he says."

He said Mattis and Kelly are not being truthful, characterizing their denials as "political statements to protect their jobs."

Watch the report above and reaction from Fox News senior political analyst Brit Hume.

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