In an excerpt from her upcoming book, Hillary Clinton said her “skin crawled” during the second presidential debate last year when Donald Trump hovered behind her while she spoke.

“Two days before, the world heard him brag about groping women. Now we were on a small stage and no matter where I walked, he followed me closely, staring at me, making faces,” Clinton said in an excerpt from her book obtained by MSNBC. “It was incredibly uncomfortable. He was literally breathing down my neck. My skin crawled.”

The memorable interaction became fodder for Saturday Night Live, and Clinton said she has since questioned whether she handled the situation well.

“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.

“I chose Option A, I kept my cool, aided by a lifetime of dealing with difficult men trying to throw me off,” she added. “I did, however, grip the microphone extra hard. I wonder, though, whether I should have chosen Option B. It certainly would have been better TV. Maybe I have over-learned 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.”

Clinton’s book, titled What Happened, is set to be released Sept. 12. She said it will address historic moments during the campaign that she remembers fondly in addition to moments she regrets.

“Every day that I was a candidate for president, I knew that millions of people were counting on me, and I couldn’t bear the idea of letting them down, but I did,” she said in the book excerpt. “I couldn’t get the job done, and I’ll have to live with that for the rest of my life.”

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Write to Katie Reilly at Katie.Reilly@time.com.