Nicolle Wallace is expanding on her well-publicized feud with Sarah Palin – whom she served as a senior adviser during her campaign for the vice-presidency – with the publication of her second novel, “It’s Classified.”

She includes a character she says was inspired by Palin – a vice presidential candidate who suffers from mental illness.

On ABC’s “Top Line” today, Wallace said she isn’t suggesting that Palin is or was mentally ill. But she said the character was sparked by erratic behaviors she witnessed from Palin on the trail – actions that she said led top McCain campaign officials to discuss whether it would be appropriate for her to sworn in as vice president should John McCain have been elected president.

“It would be absurd for me to diagnose Sarah Palin with a sprained ankle, let alone any sort of mental illness,” Wallace told us. “I wasn’t the only one that saw Sarah Palin vacillate between glorious highs on the campaign trail – and, you know, while she was speaking and at the convention — to really troubling lows when she seemed stumped in interviews.”

“And then in private it was more serious than that. She was incredibly withdrawn, seemed deeply troubled, and I didn’t know what the problem was, but those behaviors concerned me. They concerned a lot of people, and we did have discussions about whether it would be appropriate from someone who seemed to swing from so high to so low, when the pressure of the campaign as placed on her shoulders, would it be appropriate for somebody like that to have to endure the burdens of the vice presidency?”

Wallace stressed, however, that those discussions never went so far as pondering legal possibilities, since the vice president is elected along with the president.

The notion that these conversations were anything other than the concern I just articulated is simply untrue. Discussions never became legal in nature or logistical in nature, because of the arc that the campaign took. As you know, the McCain campaign fell behind the Obama campaign by very dramatic numbers, and it became very, very unlikely that we would have prevailed, so those conversations didn’t go on for long.”

Wallace said her book also draws on her experience inside the Bush White House during the Valerie Plame leak investigation.

“The town becomes a snake pit. Everyone has lawyers. You can’t trust anybody, and that’s a little bit what happened when our White House was investigated. The Valerie Plame investigation left scars on all of our psyches. And so there’d been all sorts of things I’d experienced, and I wanted to just play with those ideas in fiction.”

As for today’s politics, Wallace said she views tonight’s debate as make-or-break for Gov. Rick Perry, whose previous debate performances have underwhelmed.

“Rick Perry — I think he started too late for somebody who hadn’t been scrutinized by or exposed to the national political environment,” she said. “I think the stakes are higher for him than anybody else. And I think that, you know, he has to stand on that stage tonight, and not just show that he can beat Mitt Romney in a debate, but show that he’s the guy that could defeat Barack Obama in a general election, because that’s what Republican’s are looking for.”