Former Democratic presidential candidate Hillary Clinton has said in a new book that Donald Trump made her skin crawl by stalking her around the stage during a 2016 campaign debate and questions whether she should have fired up and told him to "back up, you creep".

Key points: Mrs Clinton questions if she "over-learned" a life lesson of staying calm as a woman

Mrs Clinton questions if she "over-learned" a life lesson of staying calm as a woman She refers specifically to a debate where Mr Trump loomed behind her as she spoke

She refers specifically to a debate where Mr Trump loomed behind her as she spoke The book What Happened is set to be released in coming weeks

In audio excerpts of the book titled What Happened that aired on US media on Wednesday, Mrs Clinton described her 2016 campaign as "joyful, humbling, infuriating, and just plain baffling" while acknowledging that she failed her millions of supporters by losing to Mr Trump in the November election.

In the excerpts, Mrs Clinton described the October 9 debate in St Louis in which Mr Trump followed her closely about the stage, lurking behind her, as she fielded questions from a live television audience.

"This is not OK, I thought," Mrs Clinton said.

"It was the second presidential debate and Donald Trump was looming behind me.

"We were on a small stage and no matter where I walked, he followed me closely, staring at me, making faces."

Mrs Clinton questions whether she should have responded more aggressively to Mr Trump's debate antics. ( Reuters: Rick Wilking )

The debate came two days after an audiotape emerged in which Mr Trump was heard bragging about groping women.

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

"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.'"

Mrs Clinton said she chose the first option.

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

Sorry, this video has expired Hillary Clinton reflects on her election campaign and Donald Trump's negotiating methods. (Image: Reuters/Brendan McDermid)

But in the book, Mrs Clinton questions whether she should have chosen the second option.

"It certainly would have been better TV," she said.

"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."

Mrs Clinton said writing the book, due to be released in the coming weeks, "wasn't easy".

"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.

"I couldn't get the job done."

Reuters