Presidential adviser Kellyanne Conway is "the number one leaker" inside the Trump White House, the author of an explosive new tell-all book told CNN's Jake Tapper on Sunday.

Ronald Kessler, author of the new book The Trump White House: Changing the Rules of the Game, appeared on State of the Union and said, "if you wonder why there are so many leaks out of the White House, one reason is Kellyanne Conway is the number one leaker."

Kessler, a seasoned writer for the Washington Post, recalled that when interviewing Conway for his book, she said "most mean, cutting and obviously untrue" about senior staffers, specifically former Chief of Staff Reince Priebus, Conway also slammed Jared Kushner and Ivanka Trump for spreading rumors about ousted adviser Steve Bannon, and, according to aides, Conway was often spotted sending nefarious texts to journalists. "There was no question of the veracity of what was happening," Kessler told Tapper. His conclusion was based on firsthand accounts relayed by Conway herself.

Kessler also wrote that Kushner and Trump were responsible for some of the most irresponsible decisions of Donald Trump's presidency, not the least of which was the firing of FBI Director James Comey last spring. Kessler refers to the president's son-in-law and daughter as "teflon aides," due to Trump's unwillingness to fire them.

"In the end, Jared and Ivanka would push the most disastrous and foolish decisions of Trump's presidency ... they had no understanding of the basic fundamentals of how government works ... most of all, they had no understanding of the political consequences of their actions."

Conway is one of Trump's longest-serving aides and has come under recent fire, having been accused of violating the Hatch Act when she endorsed Alabama Senate Candidate Roy Moore last fall. The Hatch Act imposes fines and possible jail time on members of the Executive Branch for engaging in certain types of political activity.

Conway responded to Kessler's claims on Fox & Friends on Monday.

"I have a great working relationship and great relationship with Jared and Ivanka. First of all, the president and I talked at length last night about a number of issues ― talked about that very briefly, because there's so many relevant things happening. He knows ... who the leakers and the liars are and have been."

"We don't need a book to tell us that Mr. Trump is going to be a great president," she added. "And I just want to say one thing, leakers get great press. I got a lot of texts and emails yesterday, 'Wow, I feel so left out. You never tell me anything.' Leakers get great press. One day ... I will have my say."

Kessler's book, The Trump White House: Changing the Rules of the Game was released on Tuesday.