Former Vice President Joe Biden believes he could have beaten 2016 Democratic presidential nominee Hillary Clinton handily in the primaries, but chose not to run out of fear of her “stop at nothing” campaign, excerpts from his new memoir revealed Wednesday.

The Daily Mail obtained exclusive excerpts of the book, “Promise Me, Dad: A Year of Hope, Hardship, and Purpose,” set for release on November 14. Although the former vice president noted that the death of his beloved son, Beau, contributed to his decision not to run for president in 2016, Biden also revealed his fear of Clinton and her vocal supporters’s ruthless methods kept him from the primaries.

“My numbers on trustworthiness, honesty, and empathy were as high as they had ever been. And I was strongest where the most formidable candidate, Hillary Clinton, was weakest: the key swing states like Pennsylvania, Ohio, and Florida,” Biden wrote.

But Clinton had been watching Biden’s every move like a hawk since 2015, the former vice president said, as she scouted out her potential competition.

“But if I ran, I told her, I would not run a negative campaign. She said the same,” Biden wrote, adding, “Although some of our supporters can get out of hand sometimes, it would not be me.”

Biden said he soon found himself at the center of a political hit job carried out by Clinton’s aggressive backers and their “fishing expeditions.”

“That was followed by a story alleging I was cozy with the banking and credit card industry when I was a senator,” Biden wrote. “And Clinton backers sent the signal that they would not stop at voting records and policies if I did get in the race.”