Tonight’s the big night – the night Sarah Palin faces off with Joe Biden in the one-and-only vice-presidential debate this election season.

Beginning at 9 PM ET tonight, the debate will be moderated by PBS’s Gwen Ifill, who has come under some criticism as to whether she will be a fair referee. Palin, John McCain’s running mate, heads into the debate with support numbers lower than they were coming out of the Republican conventions early last month.

An  Associated Press-Gfk poll released Wednesday found that just 25 percent of likely voters believe the Alaska governor has the right experience to be president. That’s down from 41 percent just after the GOP convention, when she made her well-received début on the national stage.

And a new Washington Post-ABC News poll shows that Palin may actually be a drag on the Republican ticket among key voter groups. After five weeks of energizing the Republican base after being chosen by McCain for the ticket, Palin’s recent performances in national interviews, such as those with CBS’s Katie Couric, is partially to blame for her falling numbers. Six in 10 voters see her as lacking the experience to be an effective president, and a third are now less likely to vote for McCain because of her, according to the Post-ABC poll.

But many Palin supporters and outside observers say not to underestimate Palin, who has cleaned the clock of others in previous Alaska debates.

"I think we’ve handled her fine. I think the criticism and attacks [on Palin] have been unprecedented," McCain said in an interview on MSNBC Thursday morning. "She’ll be fine tonight … when it’s her and the American people, she’s fine … I’m proud of her record and I’m proud of her."

Meanwhile, aides to Biden – Barack Obama’s running mate – have been huddling at a hotel in Wilmington, DE, to prepare, and Biden has been seeking the advice of some very high-profile women.

The Washington Post reports that the study group threw him questions he may have to field tonight, reviewed tapes of Palin’s debate and tried to prepare for any contingency that may arise.

But strategists in both parties say the famously garrulous Biden must be mindful that Palin is a woman.

The Delaware senator has spoken with longtime friends, including Geraldine Ferraro, and Sens. Hillary Clinton, D-NY, and Barbara Boxer, D-CA, about how to approach the debate. His advisers brought in a female politician in her 40s, Michigan Gov. Jennifer Granholm, to stand in for Palin in the practice sessions.

But Biden is relying on one person, in particular, who has known him since he had a stutter — his sister.

"He’s been my best friend all my life," Valerie Biden Owens told The New York Times. "I opened my eyes and he was there and he said, ‘Let’s go.’ I was his sidekick."

Biden Owens, 62, remembers her big brother as “Joey.” She has managed every one of his campaigns, from high-school class president to his New Castle County Council race to his first Senate bid, a 1972 upset victory, to his minefield of a presidential run in 1988. Although this is the first time she has had no official position on her brother’s campaigns, she’s still acting as an informal adviser – both professionally and personally.

"She is absolutely his political alter ego and confidante," said Biden spokesman David Wade. "She talks with the campaign every day."

It was Biden Owens who endorsed the plan to have her brother practice with Granholm, and who offered him tips on how to handle himself in tonight’s debate so he doesn’t overpower Palin.

"They finish each other’s sentences — they’re the yin and yang of the Biden family," said Marjorie Margolies-Mezvinsky, a longtime friend.