(CNN) President Donald Trump's niece Mary Trump -- a psychologist whose recently published book criticizes the President and his family -- asserted Friday that her uncle's childhood is affecting his ability to govern in a crisis.
"Donald is a psychologically deeply damaged man, based on his upbringing and the situation with his parents," she told CNN's Chris Cuomo on Friday on "Cuomo Prime Time."
"He is not going to get better and he is without question going to get worse," she added.
The stinging assertion is another blistering comment from one of Trump's family members who has been interviewed often this week after her book, "Too Much and Never Enough: How My Family Created the World's Most Dangerous Man," went on sale. The book paints the President in an unflattering light and traces his governing style back to his childhood.
When asked if the President was known among family members as someone who didn't tell the truth, Mary Trump asserted that he "does on some levels know what he's doing" and pointed to issues such as not wearing a mask. She said her uncle is not anti-science but will ignore facts in order to spin his preferred narrative.
"I think one of the reasons he's sort of unraveling a bit now is because what he's always done in the past, that used to work, isn't really working as effectively anymore, so it has him scrambling a bit," she said.
"Knowing, not knowing; educated, not educated as you say -- ultimately it is irrelevant," Mary Trump added. "Just as in the grand schemes of things -- although I think it's extremely useful in some ways to understand his psychology -- it's irrelevant compared to what he's doing, that's what we need to focus on."
Trump, after days of silence about her, called her "a mess" earlier on Friday and alleged that she wrote "untruthful things."
In a series of tweets Friday, he accused her of breaking an unspecified law and lambasted her for criticizing his parents who, he added, "couldn't stand her!"
Mary Trump, in turn, asserted that she was legally in the right.
"I never had Donald's tax returns in my possession, so I could not have revealed them to anybody," she told Cuomo.
She and her grandmother "were very close," she said. "I really loved (my grandmother) and believe that she loved me. My grandfather, I don't think was really, had real positive feelings towards anybody except perhaps Donald."
She called the assertion that she was a mess "an attack he hurls, predominantly, I think, about women."
"Honestly, I'm in very good company," she added. "I believe he's said the same thing about Nancy Pelosi, and I'm fine with that."
She has faced litigation from Robert Trump, the President's brother, who argued in court that the book violated a confidentiality agreement related to Fred Trump's estate. But a New York judge ultimately allowed its release. It sold a staggering 950,000 copies by the end of its first day on sale, publisher Simon & Schuster said Thursday.
Mary Trump has made damning allegations against the President in recent TV appearances, including claiming she's heard Trump use racial slurs. The White House has denied her claims.
In the series of tweets Friday, Trump also had choice words for John Bolton, calling his former national security adviser a "lowlife dummy." Bolton recently published a book about his time in the White House and called the President "naive and dangerous."
The President wrote: "I am the ultimate member of The Book of the Month Club. First I have lowlife dummy John Bolton, a war mongering fool, violating the law (he released massive amounts of Classified Information) and an NDA in order to build badly needed credibility and make a few dollars, which will all end up going to the government anyway."
"Many books have been written about me, some good, some bad. Both happily and sadly, there will be more to come!," the President wrote, in conclusion.
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