Mrs Harris, who would lose the election to Donald Trump, has addressed this period in her most pointed attack on President Biden.
In her new book, published by The Atlantic, she wrote: "It's Joe and [Former First Lady] Jill's decision. We all said that, like a mantra, as if we'd all been hypnotised.
"Was it grace, or was it recklessness? In retrospect, I think it was recklessness. The stakes were simply too high.
"This wasn't a choice that should have been left to an individual's ego, an individual's ambition. It should have been more than a personal decision."
Vice President Harris also questioned if she should have spoken out, as she said she felt "growing panic" about Biden's capabilities.