Transcript for President Trump’s niece, Mary Trump, says ‘everything’s about money in the family’
He's utterly incapable of leading this country, and it it's dangerous to allow him to do so. That's the president's estranged niece, Mary trump. Speaking out for the first time since publishing a sad, scathing memoir about her family, including her uncle, Donald Trump. My colleague, George Stephanopoulos sat down with her for her first interview. She is the daughter of Fred trump Jr., he was a pilot for twa and a long strug with alcoholism, die at the age of 42. Along with her decades of living on the margins of the trump dynasty. I didn't write it as a form of therapy or anything like that. In fact, I would have preferred not to write it. It was quite difficult. The book is absolutely Bourne of the family dysfunction. It's the first time a family member has broken rank, offering a look at what shaped the 45th president. The was published despite legal attempts to prevent it from ever seeing the light of day. Mary's cousin Eric Trump simply tweeting "Every family has one." Why didn't you write the book three years ago? I thought long and hard about saying something. I knew if I had said anything I would have been painted as a disgruntled, disinherited niece who just wanted her 15 minutes, which obviously is being said about me now. That's exactly what the white house says, basically you're lying for money. If I had wanted money or revenge I would have done their ten years ago. Your brother's not happy with the book. This is entirely my doing. I didn't consult anybody in my family. Nobody knew it was happening, I didn't feel that I needed to ask permission by any stretch of the imagination, but I didn't want to implicate anybody. I believe very strongly it's my obligation. While today she's being characterized as the family's outcast, there was a short time when Mary trump worked directly with her uncle Donald Trump who briefly took her on to write "The art of the come back." I thought my goal was to tell the story of how he regrouped, pulled himself up by his bootstraps. While researching the book there was a trip to mar-a-lago. You describe a scene. I went to the table wearing shorts and a bathing suit and he looked up and commented on my appearance in a way that was really shocking to me. He exclaimed something and then said, "Mary, you're stacked", or something like that. And I grabbed the towel and put it around my shoulders. Mary says the person who shaped the future president the most was his father, whom she describes as a sociopath. He had no empathy. He was incredibly driven in a way that turned other people, including his children, his wife, into pawns. To be used to his own ends, and, in my father's case, tragically, he was not of use. Mary says her father, Fred Jr. Was the heir apparent to the business until he rejected his eldest son. You wrote, Donald, destroyed my father. That was harder to write. Partially, because my dad, he was kind, generous, fiercely loyal and beloved. You say that was the hard sentence to write. I lift out the next sentence. I can't let him destroy my There are so many parallels between the circumstances in which my family operated and in which this country is now operating. The collateral damage that can be created by allowing somebody to, to live their lives without accountability. And it is striking to see that continuing now on a much grander scale. The family's business empire has been shrouded in secrecy for decades. The president has never released his tax returns, defying tradition. But Mary trump would help blow the lid off some of the family finances, providing 19 boxes full of decades of tax records she obtained in litigation with the family. You didn't know what was in the documents, really? I had no idea. They seemed to think that it was extremely valuable. And I knew that they knew what they were doing. The "New York Times" reporting revealing Fred senior's net worth was far greater than previously estimated and that far more of the president's wealth was attributable to his father than had been previously known. The documents revealing accounting practices by Donald and his siblings that many think could be tax fraud. It was designed to siphon money away from my grandfather's very valuable and successful company so the money could be disappeared and the money Lett to pay taxes on was significantly less. The president unscathed by the bombshell revelations. For most of us, our mistakes are cumulative. When there's a reckoning, the sum total of what we've done is taken into account. That does not seem to exist in Donald's universe. But for you, the political become personal, the personal has become political. Yes. You write, "I had to take Donald down." Yes, maybe a bit of an overstatement there in the sense that I didn't ever think that there was any one thing I or mib anybody else could do, but certainly in that moment I'm describing, I felt I needed to do anything I could to stop this and also to make up for the fact that I didn't do anything in the past. What do you want to happen This country is on a precipice, and people immediate need to know. People need as much as possible to make a decision that makes sense for our future. Her final words for the president, unvarnished and stark. And if you're in the oval office today, what would you say Resign. You can stream the full,
This transcript has been automatically generated and may not be 100% accurate.