'He Is Utterly Incapable of Leading': President's Niece Breaks Silence on Tell-All the Family Hates

She speaks.

In her first interview since news last month that she was releasing a tell-all about her family, Donald Trump's niece Mary Trump sat down with ABC News' George Stephanopoulos on Tuesday to discuss her immediate bestseller — which describes the president in unsparing terms.

Mary was no less blunt in her talk with Stephanopoulos, which first aired on World News Tonight. (More will air on Good Morning America on Wednesday.)

"He is utterly incapable of leading this country and it's dangerous to allow him to do so ... based on what I've seen my entire adult life," Mary, 55, told Stephanopoulos about her uncle, the president.

Elsewhere in the interview, she looked back at a 2017 trip to the White House, also recounted in her book, when she spoke briefly with President Trump.

"That was four months in. He already seemed very strained by the pressure," she said. "He'd never been in a situation before where he wasn't entirely protected from criticism or accountability or things like that."

Mary told Stephanopoulos, "I just remember thinking: He seems tired, he seems — this is not what he signed up for, if he even knows what he signed up for."

Asked what she would tell her uncle if she saw him in the Oval Office today, she replied, "Resign."

RELATED: White House Insists Trump Didn't Cheat on His SATs After Niece Claims Otherwise in Memoir — 'Absurd'

Mary's Too Much and Never Enough was released on Tuesday.

Publisher Simon & Schuster has said it printed more than 600,000 copies of the No. 1 title on Amazon, citing "high demand and extraordinary interest" after the president's younger Robert Trump sued to stop Mary, citing a confidentiality agreement she signed in 2001 over a family lawsuit about money.

A judge on Monday ruled against Robert — paving the way for her memoir's release and for her to start talking about it.

Mary, among other scathing accounts of President Trump's behavior, writes how the root of his sociopathic dysfunction lies with his father, patriarch Fred Trump Sr., who she says suffered from the same set of toxic psychological behaviors.

By contrast, Mary believes her dad, Fred Trump Jr., was too sweet-souled to survive them; he died at 42 in 1981 after years of heavy drinking.

Too Much and Never Enough covers President Trump's childhood, early life, schooling and business career, with allegations from Mary that he cheated on his SATs, didn't visit his dying brother in the hospital and other behavior.

Elsewhere in the book, Mary details how she secretly sent extensive records produced as a result of a 20-year-old lawsuit over patriarch Trump Sr.'s estate to The New York Times for a 2018 investigation into her family's finances.

RELATED: Trump Niece's Tell-All Describes a Family of Liars, Cheats & Abusers Who Destroyed Her Dad

Dimitrios Kambouris/WireImage; Mary Trump/Twitter From left: Robert Trump and Mary Trump

Simon & Schuster Front cover of Mary Trump's soon-to-be-released tell-all, "Too Much and Never Enough"

"No one knows how Donald came to be who he is better than his own family," Mary writes early on in her book. "Unfortunately, almost all of them remain silent out of loyalty or fear. I'm not hindered by either of those."

"Donald's monstrosity is the manifestation of the very weakness within him that he's been running from his entire life," she writes. "For him, there has never been any option but to be positive, to project strength, no matter how illusory, because doing anything else carries a death sentence; my father's short life is evidence of that."

"But," according to Mary, "he can never escape the fact that he is and always will be a terrified little boy."

The White House in turn has called the book full of "falsehoods," and Robert said it was a "disgrace."

“Her attempt to sensationalize and mischaracterize our family relationship after all of these years for her own financial gain is both a travesty and injustice to the memory of my late brother, Fred, and our beloved parents," he said in June, according to The New York Times.

"I and the rest of my entire family are so proud of my wonderful brother, the president, and feel that Mary’s actions are truly a disgrace,” he said then.

SAUL LOEB/AFP via Getty Images President Donald Trump

A White House spokeswoman said in a separate statement last week: "Mary Trump and her book’s publisher may claim to be acting in the public interest, but this book is clearly in the author’s own financial interest."

"President Trump has been in office for over three years working on behalf of the American people — why speak out now?” the spokeswoman said, continuing: “The President describes the relationship he had with his father as warm and said his father was very good to him. He said his father was loving and not at all hard on him as a child."

Mary's brother, Fred Trump III, who once sued his aunts and uncles alongside her over Trump Sr.'s estate, has also disavowed her book.

In a statement from the Trump Organization, he said, "My wife, children and I have a strong relationship with our extended family. We had no involvement with the preparation of this book, which is a breach of trust and a violation of our privacy."

Simon & Schuster, meanwhile, called Too Much and Never Enough "a work of great significance, with very real implications for our national discourse."