Challenged over explosive new book, Mary Trump claims 'deep experience' inside Trump family

President Trump's niece appeared on ABC's "The View" on Thursday.

Strongly challenged on Thursday over why readers should believe her explosive claims about President Donald Trump and his family, Mary Trump – the president’s niece – insisted that her new book comes from “very deep experience within the family.”

“I’m not some stranger writing it, I’m his niece,” Mary Trump said in a daytime television exclusive interview on ABC’s “The View.”

In the past week, the new book, titled "Too Much and Never Enough: How My Family Created the World's Most Dangerous Man," has sold more than 1.35 million copies, according to publisher Simon and Schuster.

But on Thursday, “The View” co-host Meghan McCain repeatedly questioned Mary Trump’s credentials as a Trump family insider.

McCain noted that Mary Trump has little to no current relationship with the Trump family, including her own cousins – the president’s children.

“If you were probably close to that family you would probably know your cousin Don Jr. and Ivanka on a level that you clearly don’t,” McCain said.

In a tweet on Friday, the president described Mary Trump as "a seldom seen niece who knows little about me."

During Thursday's episode of "The View," McCain bluntly told the president’s niece: “I don’t like family tell-all books … because they’re told from the one side, and often the subjects are villainized to the point that I don’t actually end up believing the stuff written.”

McCain, daughter of the late Sen. John McCain, R-Ariz., noted that “there have been books written about my family which are complete and total garbage … [but] at the end of the day you get a really good paycheck out of it.”

In response, Mary Trump noted that her relationship with her “much younger” cousins is “irrelevant” to the “foundational” story she’s telling about “how Donald became the person he is.”

She said that if she wanted to “cash in” she would have written a book 10 years ago, when she was not taking “the risk” of targeting a sitting U.S. president.

“But I felt it was extremely important that the American people have all of the information they need in order to make an informed decision” about the president as he seeks reelection, Mary Trump said.

Her book presents a scathing depiction of the sitting president, largely drawing, Mary Trump says, from the author’s own memories, conversations with family members, and legal, financial and family documents.

As Mary Trump tells it, Donald Trump grew up in a "dysfunctional" family whose own family members were used as “pawns” and believed “money stood in” for acts of love.

She previously told ABC News “it’s impossible to know who Donald might have been” had he been born into a different family, but his father, Fred Trump, was a “sociopath” who pushed his children to “succeed at all costs,” to view people as “expendable,” and to “do anything to get attention, financial rewards, and to ‘win.’”

That has created a “dangerous situation” for America, she said.

In her interview with “The View” on Thursday, Mary Trump said the president’s family “excels at” being “gratuitously cruel.”

According to her account, tensions within the family reached a boiling point in 1999, after her grandfather died and she learned that he had essentially cut her and her brother out of his will. When she and her brother then filed a lawsuit, the rest of the family sought “to cause us more pain and make us more desperate," ending the medical insurance they had always received through their grandfather’s company, Mary Trump wrote in her book.

They eventually reached a settlement.

On Thursday, Mary Trump also claimed she heard Donald Trump and others in the family use “the n-word” as a "generalization."

“It wasn’t unusual in the family,” she said, adding that while growing up she “never [knew] anybody in my family actually to interact with a person of color.”

The White House has disputed such claims and dismissed the book as a work full of "falsehoods" and "absurd allegations."

"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 self-interest," the White House said in a statement.

"President Trump has been in office for over three years working on behalf of the American people – why speak out now? 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," the statement continued.

ABC News’ Lucien Bruggeman, Nadine Shubailat and John Santucci contributed to this report.