Some excerpts courtesy of NYT:

His “Big Brain”:

As a high school student in Queens, Ms. Trump writes, Donald Trump paid someone to take a precollegiate test, the SAT, on his behalf. The high score the proxy earned for him, Ms. Trump adds, helped the young Mr. Trump to later gain admittance when he transferred as an undergraduate to the University of Pennsylvania’s prestigious Wharton business school.

Mr. Trump has often boasted about attending Wharton, which he has referred to as “the best school in the world” and “super genius stuff.”

His lack of principles:

Even at the start of Mr. Trump’s campaign, his sister, Maryanne Trump Barry, a retired federal appeals court judge, had deep reservations about his fitness for office, Ms. Trump writes.

“He’s a clown — this will never happen,” she quotes her aunt as saying during one of their regular lunches in 2015, just after Mr. Trump announced that he was running for president.

Maryanne Trump was particularly baffled by support for her brother among evangelical Christians, according to the book.

“The only time Donald went to church was when the cameras were there,” Ms. Trump quotes her aunt as saying. “It’s mind boggling. But that’s all about his base. He has no principles. None!”

His mental illness:

Ms. Trump, a clinical psychologist, asserts that her uncle has all nine clinical criteria for being a narcissist. And yet, she notes, even that label does not capture the full array of the president’s psychological troubles.

“The fact is,” she writes, “Donald’s pathologies are so complex and his behaviors so often inexplicable that coming up with an accurate and comprehensive diagnosis would require a full battery of psychological and neurophysical tests that he’ll never sit for.”

At another point she says: “Donald has been institutionalized for most of his adult life, so there is no way to know how he would thrive, or even survive, on his own in the real world.”

Like other critics of the president, Ms. Trump takes issue in the book with the notion that Mr. Trump is a strategic thinker who operates according to specific agendas or organizing principles.

“He doesn’t,” she writes. “Donald’s ego has been and is a fragile and inadequate barrier between him and the real world, which, thanks to his father’s money and power, he never had to negotiate by himself.”

WaPo has this to add:

Donald escaped his father’s contempt, Mary Trump writes, because “his personality served his father’s purpose. That’s what sociopaths do: they co-opt others and use them toward their own ends — ruthlessly and efficiently, with no tolerance for dissent or resistance.”

The president, Mary Trump says, is a product of his domineering father and was acutely aware of avoiding the scorn that Fred Sr. heaped on the older brother, called Freddy. “By limiting Donald’s access to his own feelings and rendering many of them unacceptable, Fred perverted his son’s perception of the world and damaged his ability to live in it.”

And this:

Mary Trump writes that her grandfather’s children routinely lied to him, but for different reasons. For her father, “lying was defensive — not simply a way to circumvent his father’s disapproval or to avoid punishment, as it was for the others, but a way to survive.”

For her uncle Donald, however, “lying was primarily a mode of self-aggrandizement meant to convince other people he was better than he actually was,” Mary Trump writes.

ABC News reveals how Trump even objectified his own niece:

In one particularly disturbing scene from a trip to Mar-a-Lago, Mary recounts how when she was 29 and wearing a bathing suit and a pair of shorts to lunch at the resort, her uncle looked up at her and remarked, “Holy shit, Mary. You’re stacked.”

“Donald!” Marla Maples said to her then-husband, slapping him on the arm.

“I was twenty-nine and not easily embarrassed, but my face reddened, and I suddenly felt self-conscious,” Mary recounts. “I pulled my towel around my shoulders. It occurred to me that nobody in my family, outside of my parents and brother, had ever seen me in a bathing suit.”

There are also stores on various news sites about how Trump abused and cheated his own family members, how he repeatedly failed at his various businesses, and how he managed to lie his way right into the White House. 

The interesting thing is that the book does not really reveal anything that we did not know, or suspect, about Donald Trump. However, it does manage to provide some context for just why Trump is such a horribly damaged human being.