"And for this I'd never forgive him".
But what stung the most, she says, was the continuous, false allegations that her husband was a secret Muslim, born overseas.
"What if someone with an unstable mind loaded a gun and drove to Washington", she wrote in her book, according to The Washington Post.
She also writes about first meeting future president Barack Obama, raising children, and working to empower girls across the globe.
"The whole thing was insane and mean-spirited, of course, its underlying bigotry and xenophobia hardly concealed", the former First Lady wrote. "Donald Trump, with his loud and reckless innuendos, was putting my family's safety at risk", she wrote.
Obama's memoir "Becoming" releases on November 13.
In her memoir, Becoming, Barack Obama's wife also denounces Mr Trump's "birther" campaign, which questioned her husband's citizenship, calling it bigoted, risky and "deliberately meant to stir up the wingnuts and kooks".
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Georgia moved up a spot to No. 5, putting it just outside the coveted top four spots for teams that will play in the semifinals. The problem is, they'll have to do it two times over to claim their 12th Big 12 title and fourth consecutive conference crown.
She also can't believe so many women voted for a "misogynist" after all Trump has said.
The book also sees her take aim at Donald Trump, denouncing him for the infamous Access Hollywood tape, where he can be heard talking about grabbing women by their vagina. She writes of Trump following Clinton around the stage, standing nearby and "trying to diminish her presence".
The comments were some of Michelle Obama's most direct aimed at the current President, whom she has mostly avoided criticising since leaving the White House past year. And memoirs by former first ladies, including Clinton and Laura Bush, are usually best-sellers.
Some accused Michelle Obama of hypocrisy.
Mrs Obama launches her promotional tour on Tuesday not at a book shop, but at Chicago's United Centre, where tens of thousands of people have purchased tickets - priced from just under 30 dollars (€26) to thousands of dollars - to attend the event moderated by Oprah Winfrey.
Widely praised as a gifted orator and communicator, Obama has long said she has no interest in running for office, although she held a few campaign-style rallies before the midterms urging people to register to vote.