A few excerpts from former FBI Director James Comey’s new book, "A Higher Loyalty," have caused a stir in the White House and a reason for President Trump to once again lash out on Twitter.

National security expert Juliette Kayyem told Boston Public Radio Friday that while Comey is a flawed, complicated character, these excerpts do show what parts of the dossier Trump was actually concerned about.

“The president is solely fixated on two paragraphs in the dossier. It is a couple dozen pages of which most of the allegations are of rampant collusion between his campaign and the Russians. He seems unconcerned about that. And unconcerned about denying it. I find that interesting,” Kayyem said.

In the book, expected to be released Tuesday, Comey compares Trump to a mob boss and recalls a meeting where the president asked him to look into the infamous pee tapes mentioned in the Steele dossier.

"He brought up what he called the 'golden showers thing' ... adding that it bothered him if there was 'even a 1 percent chance' his wife, Melania, thought it was true ... In what kind of marriage, to what kind of man, does a spouse conclude there is only a 99 percent chance her husband didn't do that?" Comey writes.

In a tweet responding to the excerpts, President Trump called Comey an “untruthful slime ball” and said “it was my great honor to fire James Comey.”

National security expert Juliette Kayyem is CEO of ZEMCAR and a contributor to CNN and WGBH. To listen to her interview in its entirety, click on the audio player above.