"I found out an hour before I went on stage with her. I think they were scared I would say something or whatever. Like the rest of the country, I had no idea who she was and I was actually crying on the bus on the way to the rally," said McCain, who is promoting her new book, "Dirty, Sexy, Politics."
"And then I found out who she was, and I remember being on stage and distinctly thinking, 'God, let her not have any skeletons in the closet. Please God.' And if you see any video footage of it, I looked panicked," se added. "I was scared, just really scared. I didn't know her. "
McCain has not been shy to express her rocky relationship with the vice presidential candidate, whom she has since described as a "time bomb" in her new book.
"It was just one thing after another," she told Leno. "In politics it's about knowing what's going to come at you and I really didn't know anything."
In her book - released late last month - McCain also takes aim at how campaign manager Steve Schmidt went about picking Palin.
"How the Palin selection process and announcement had been handled seemed to highlight things that were innately wrong with our campaign and with the tactics of Steve Schmidt, she wrote. "It was a risky move-one of those things that can wind up being genius or the stupidest decision of all time."
Schmidt and Palin had a now-famous contentious relationship, capped off late last year when the former Alaska governor repeatedly questioned his competence in her autobiography. For his part, Schmidt has said Palin would prove "catastrophic" to the GOP if she was the nominee in 2012.
Meanwhile, when it comes to whether McCain would support a potential Palin presidential bid in 2012, she said her heart actually belongs to another likely White House hopeful.
"I am so sick of this us-versus-them mentality," she said. "I just want a candidate that's going to stop being us versus them. So right now I am team Romney."
Her comments came shortly before the release of a new CNN/Opinion Research Corporation poll showing more 52 percent of Americans hold an unfavorable view of the former Alaska Republican while 38 percent have a positive view.
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