US President Donald Trump’s niece offers a scathing portrayal of her uncle in a new book that credits a “perfect storm of catastrophes” for exposing the president at his worst.

Mary L Trump, a psychologist, writes that the coronavirus pandemic, the possibility of an economic depression and deepening social divides have brought out the “worst effects” of Donald Trump’s pathologies.

Those factors, along with “Donald’s penchant for division, and uncertainty about our country’s future have created a perfect storm of catastrophes that no one is less equipped than my uncle to manage”, she writes in Too Much and Never Enough, How My Family Created The World’s Most Dangerous Man.

Mary Trump is the daughter of Trump’s older brother, Fred Jr, who died after a struggle with alcoholism at 42.

In the book, Mary Trump makes several revelations, including alleging that the president paid a friend to take the SATs – a standardised test widely used for college admissions – in his place.

She writes that his sister Maryanne had been doing his homework for him, but she couldn’t take his tests.

Mary L Trump has written the tell-all about her uncle President Donald Trump.

Donald Trump worried that his grade point average, which put him far from the top of the class, would “scuttle his efforts to get accepted” into the Wharton School of the University of Pennsylvania, which he transferred to after two years at Fordham University in the Bronx.

“To hedge his bets he enlisted Joe Shapiro, a smart kid with a reputation for being a good test taker, to take his SATs for him,” she writes.

“That was much easier to pull off in the days before photo IDs and computerised records. Donald, who never lacked for funds, paid his buddy well.”

And Mary Trump writes, in awe, of Trump’s ability to gain the support of prominent Christians and white Evangelicals.

“The only time Donald went to church was when the cameras were there. It’s mind boggling. He has no principles. None!”

Mary Trump traces much of her pain to the death of her father, who died when she was 16, and her grandfather Fred’s penchant, as she describes it, to sew division in the family.

“The atmosphere of division my grandfather created in the Trump family is the water in which Donald has always swum, and division continues to benefit him at the expense of everybody else.

“It’s wearing the country down, just as it did my father, changing us even as it leaves Donald unaltered,” she wrote.

“It’s weakening our ability to be kind or believe in forgiveness, concepts that have never had any meaning for him.”

Publisher Simon & Schuster announced on Monday they would be publishing the book two weeks early, on July 14, citing “extraordinary interest”.

The revised date came after a New York appellate court cleared the way for the book’s publication following a legal challenge.