Former Democratic presidential candidate Hillary Clinton wrote that then-Republican candidate Donald Trump had invaded her personal space during a presidential debate in her new book, 'What Happened?'

The allegation was reported on MSNBC.

Trump, who went on to win the election and become President of the United States, stood behind Clinton during the second presidential debate in St. Louis on October 9, 2016.

"No matter where I walked, he followed me closely, staring at me, making faces," Clinton wrote. "It was incredibly uncomfortable."

"My skin crawled," she added.

She continued: "It was one of those moments where you wish you could hit pause and ask everyone watching, 'Well, what would you do?' Do you stay calm, keep smiling and carry on as if he weren't repeatedly invading your space? Or do you turn, look him in the eye, and say loudly and clearly, 'Back up you creep, get away from me! I know you love to intimidate women, but you can't intimidate me, so back up.'"

"I chose option A. I kept my cool, aided by a lifetime of dealing with difficult men trying to throw me off.

Clinton wondered "whether I should have chosen option B?"

"Maybe I have overlearned the lesson of staying calm, biting my tongue, digging my fingernails into a clenched fist, smiling all the while determined to present a composed face to the world," she said.