Hillary Clinton said her "skin crawled" when President Trump stood behind her as she answered questions during the second presidential debate last year, she reveals in her new book.

In an excerpt from her forthcoming memoir "What Happened" obtained and broadcasted by MSNBC's "Morning Joe" on Wednesday morning, Clinton details her thinking during the second debate, which took place at Washington University in St. Louis one month before the election.

"It was incredibly uncomfortable. He was literally breathing down my neck. My skin crawled," Clinton writes. "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.'"

Clinton said she ultimately decided to remain calm, as her decision was "aided by a lifetime of dealing with difficult men trying to throw me off."

The former Democratic presidential nominee also detailed why she decided to write a memoir on the 2016 presidential election.

"I want to pull back the curtain on an experience that was exhilarating, joyful, infuriating, and just plain humbling," Clinton said. "Every day I was a candidate for president, I knew millions of people were counting on me. And I couldn't bear the idea of letting them down. But I did. I couldn't get the job done, and I'll have to live with that for the rest of my life."