"Rarely does a politician get a second chance to make a first impression but this could be one of those times," said CBSNews.com senior political editor Vaughn Ververs. "The bad news for the Republican campaign is that more and more Americans are telling pollsters that they have a negative impression of Palin. The good news is that because of her relatively low-level of exposure, she has a chance to turn that around when she's in front of them for 90 minutes -- or at least stop the slide."
An AP-Gfk poll released Wednesday found that just 25 percent of likely voters believe Palin has the right experience to be president. That's down from 41 percent just after the GOP convention, when the Alaska governor made her well-received debut on the national stage.
Meanwhile, according to a new CBS News poll, opinions of Palin are now evenly divided, with her unfavorable rating (33 percent) now slightly higher than her favorable rating (32 percent). Last week, Palin had an eight point net positive rating. Biden's favorable rating stands at 34 percent and his unfavorable rating at 19 percent.
Women's perception of Palin has become increasingly negative,. On Sept. 8th, Palin had a 47 percent favorable rating among women and a 19 percent unfavorable; now her favorable rating among the group is down to 30 percent, while her unfavorable has risen to 34 percent.
Thursday night's debate in St. Louis gives Palin a chance to overcome the doubts in a 90-minute showcase, her first lengthy give-and-take session since joining the GOP ticket with presidential candidate John McCain.
McCain on Thursday dismissed suggestions that he was upset with campaign staff for holding back Palin from extensive questioning by reporters and voters and not letting her be herself on the campaign trail. In the four weeks since she was nominated by party delegates, Palin has appeared without McCain at six rallies and other major campaign events. She has appeared with McCain at 15.
"We let Sarah be Sarah. She's smart, she's tough, she's been in debates before," McCain told "Fox & Friends" on Fox News Channel. "The American people ... the more they see of her, the more they love her, and I'm confident of that at the end."
If Palin is accused of saying too little since joining the ticket, Biden, in his past, has said too much, reports CBS News correspondent Jeff Glor.
Unlike his Republican counterpart, Biden has not been shy about talking to reporters, but comments he has made since Obama chose him last month have presented Democrats with their own problems and revived the longtime senator's reputation for gaffes, according to the Washington Post.
"I think Joe obviously has a challenge tonight. The expectations are so low for Sarah Palin and it's difficult for him, I think. No matter what he does he's going to be criticized," Sen. Claire McCaskill, D-Mo., said. "Sarah Palin will be tough tonight. She's a good debater, she's an effective communicator, and she knows how to throw a punch with a velvet glove and a smile on her face."
In a conference call Wednesday with reporters, McCaskill was blunt about Biden's potential for error: "My friend Joe Biden has a tendency to talk forever and sometimes say stuff that's kind of stupid." Asked to clarify her remarks, McCaskill said she meant them "affectionately."
Palin has granted just a handful of interviews and has often appeared to be uninformed about national issues. McCain and other Republicans have criticized the questions that produced this impression as "gotcha journalism."
In a CBS News interview aired Wednesday she criticized the Supreme Court's Roe v. Wade decision that legalized abortion but was unable to name any other Supreme Court decision she disagreed with, though she said there were other decisions that divided Americans.
"I think it should be a states' issue not a federal government, mandated, mandating yes or no on such an important issue," said Palin, who opposes abortion except in cases where the pregnancy threatens the woman's life.
Asked what other Supreme Court decisions she disagrees with, she replied:
"Well, let's see. There's, of course, in the great history of America rulings there have been rulings, that's never going to be absolute consensus by every American. And there are, those issues, again, like Roe v. Wade where I believe are best held on a state level and addressed there. So you know, going through the history of America, there would be others but ...."
Asked again to name another decision she disagreed with, Palin replied: "Well, I could think of, of any again, that could be best dealt with on a more local level. Maybe I would take issue with. But you know, as mayor, and then as governor and even as a vice president, if I'm so privileged to serve, wouldn't be in a position of changing those things but in supporting the law of the land as it reads today."
In a separate CBS News interview, Biden said Roe v. Wade was a good decision "because it's (as) close to a consensus that can exist in a society as heterogeneous as ours." Asked to name high court rulings he disagrees with, Biden cited the decision that struck down a law giving abused women the right to sue their tormentors in federal court.
Meantime, the Democratic National Committee has e-mailed news stories to reporters describing Palin's able performances in Alaska gubernatorial debates in 2006, part of the party's effort to dispel the notion that Palin is a sub-par debater.
One Republican saw the debate as a chance for Palin to dispel doubts about her.
"People will have a chance to see her from beginning to end without being edited," former Sen. Fred Thompson, R-Tenn., told CBS' The Early Show on Thursday.
"We've all had bad days," Thompson said, "and she's had some bad moments in some of these interviews, just like the rest of us have had."
Palin has been preparing at McCain's retreat in Sedona, Ariz. Biden has prepped near his home in Wilmington, Del., though he went to Washington for Wednesday night's vote on the economic rescue package.
The 90-minute televised debate at Washington University in St. Louis will be moderated by PBS anchor Gwen Ifill. Ifill herself was criticized by some conservatives because she is writing a book, "The Breakthrough: Politics and Race in the Age of Obama," on how politics in the black community have changed since the civil rights era. She has said she has yet to write the chapter on Obama and questioned why people think it will be favorable toward the Democrat.
"Frankly, I wish they had picked a moderator that isn't writing a book favorable to Barack Obama," McCain told Fox News on Thursday. "But I have to have confidence that Gwen Ifill will treat this as a professional journalist that she is."