No doubt the president and his allies will dispute many details of “Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man.” The new book by President Trump’s niece, Mary L. Trump, purports to be the ultimate insider’s account of a family where cruelty was passed down like an heirloom rocking chair from generation to generation.

But there is also a universality in her reminder that what fathers bequeath their sons is complicated — not least for those who would be president.

Mary Trump, who has a doctoral degree in clinical psychology, is the daughter of the president’s older brother, Fred Jr., who died at 42 from an alcohol-related illness. According to her book, the family sent her father to the hospital alone on the night of his death.

In her telling, Donald Trump’s character was warped by a desperate desire to win the nearly unattainable approval of his father, Fred Trump Sr. Nothing, including lying or cheating, was considered out of bounds. Mary Trump claims Donald Trump even enlisted a smarter kid to take his SATs for him.

All of which Mary Trump lays at the feet of her grandfather. “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,” she wrote.

We expect our presidents to be father figures, but our history is replete with examples of how they themselves never really escape the shadows of their own.

Some of them — John F. Kennedy comes to mind — were carrying out the ambitions of fathers who were overbearing and controlling. Others, such as George W. Bush, so idealized their fathers (Bush called the 41st president “close to perfect” in a eulogy at his funeral) that at times their own decisions were called into question. The younger Bush was not able to shake doubts over whether he went to war with Iraq because he viewed Saddam Hussein as a threat to this nation’s security or because he saw the Iraqi leader as “a guy that tried to kill my dad at one time.”

On the other hand, it was the absence of a father that complicated the struggles of others, including Bill Clinton and Barack Obama, to find their own identities.

Obama’s 1995 memoir, “Dreams from My Father,” is a voyage of self-discovery that culminates in Kenya, the homeland of Barack Obama Sr., where the future president realizes “how even in his absence his strong image had given me some bulwark with which to grow up, an image to live up to or disappoint.”

For Clinton, the death of his father in a car accident three months before he was born explains both the first-of-his-generation urgency of his ambition and perhaps the recklessness of his private behavior. “My father left me with the feeling that I had to live for two people, and that if I did it well enough, somehow I could make up for the life he should have had,” Clinton wrote. “And his memory infused me, at a younger age than most with a sense of my own mortality. The knowledge that I, too, could die young drove me both to try to drain the most out of every moment of life and to get on with the next big challenge. Even when I wasn’t sure where I was going, I was always in a hurry.”

Still, there are instances where presidents have found object lessons in the flaws of their fathers.

Ronald Reagan believed that his character was shaped at the age of 11, when he came home to the humiliating spectacle of his alcoholic dad passed out in the snow on his front porch, reeking of whisky from a speakeasy.

“I wanted to let myself in the house and go to bed and pretend he wasn’t there,” Reagan wrote. “... But someplace along the line to each of us, I suppose, must come that first moment of accepting responsibility. If we don’t accept it (and some don’t), then we must just grow older without quite growing up.” The boy took a fistful of Jack Reagan’s overcoat, and dragged him upstairs to bed.

So what to make of Fred Trump and his influence on the man who currently sits in the Oval Office? If Donald Trump had had a different kind of father, might he have turned out to have been a better person?

What Mary Trump offers in her book, which is a bestseller even before its release, is not so much a revelation about Trump as an explanation. The heartlessness she claims was drilled into him as a young man by his father is consistent with what we see every day. So no matter how hard the president tries to deny what she has written (White House press secretary Kayleigh McEnany characterized it as “a book of falsehoods”), readers will likely see its fundamental truth.

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