NEW YORK (AP) -- Sarah Palin is heading into her debate with Joe Biden, easily the most-anticipated vice presidential faceoff ever, weighed down by fresh evidence that voters are developing serious doubts about her readiness for the job.
A new 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.
There's a potential bright side: Thursday night's debate in St. Louis gives her a chance to overcome the doubts in a 90-minute showcase, the first time most Americans outside Alaska will see her in a lengthy give-and-take session.
The downside: A poor performance debating Biden, the Delaware senator, former presidential candidate and longtime foreign policy expert, could cement a negative image for the rest of the campaign.
Palin has been preparing at Republican presidential candidate John McCain's retreat in Sedona, Ariz.
Biden was doing his own intensive preparation near his home in Wilmington, Del., though he was going to Washington for Wednesday night's vote on the economic rescue package.
As for Palin's prospects, "the expectations are set so low for her, she could fake everyone out," said Scott Reed, who managed the presidential campaign of Republican Bob Dole in 1996.
"Palin needs to clear the bar and reframe the debate around Barack Obama and his tax and spend record," he said. "She's got to show a grasp on the issues and she's got to talk about Obama. Most importantly, she's a reformer. She's got to get back to that."
Democrats, meanwhile, were doing what they could to dispel the notion that Palin is a sub-par debater. The Democratic National Committee e-mailed news stories to reporters describing her able performances in debates in 2006 when she was running for Alaska governor.
And Missouri Sen. Claire McCaskill, one of Obama's most prominent surrogates, tried to lower expectations for Biden on a conference call with reporters.
"My friend Joe Biden has a tendency to talk forever and sometimes say stuff that's kind of stupid," McCaskill said.
Asked to clarify her remarks, McCaskill said she meant them "affectionately."
In an emotional twist, Biden's son, Delaware Attorney General Beau Biden, was to deploy this week for Iraq, where he'll serve a year as a member of the state's Army National Guard.
In the new poll, the declining sentiment for Palin was noticeable even among Republican likely voters: Just 47 percent now believe she has the right experience to be president, down from 75 percent in the previous survey. Initially, Palin's selection was widely praised by Republicans and especially conservative voters who have been wary of McCain.
The poll of 808 likely voters was conducted Saturday through Tuesday and had a sampling error of 3.4 percentage points.
A series of interviews with CBS News anchor Katie Couric recently raised questions about how well-informed she is on a range of issues the next president will face.
In a segment that aired Tuesday, Palin declined to cite a newspaper or magazine when asked what she had read regularly before McCain picked her as his running mate, saying only that she had read "most of them."
Pressed for an example, Palin told Couric: "I have a vast variety of sources where we get our news, too. Alaska isn't a foreign country, where it's kind of suggested, 'Wow, how could you keep in touch with what the rest of Washington, D.C., may be thinking when you live up there in Alaska?' Believe me, Alaska is like a microcosm of America."
In an interview Wednesday with NPR, McCain said he had turned to his running mate for advice many times. And in a testy exchange with the Des Moines Register editorial board Tuesday, amid questions about Palin's credentials, McCain replied, "If there's a Georgetown cocktail party person who, quote, calls himself a conservative who doesn't like her, good luck." Palin has echoed the anti-Washington sentiment, telling Couric the tough coverage she's received is attributable to "media elite, the Washington elite" not knowing who she is, rather than her gender.
The 90-minute televised debate was to take place at Washington University in St. Louis, with PBS anchor Gwen Ifill serving as moderator.
Ifill herself has come under criticism as the moderator from some conservatives because she is writing a book on blacks and politics, with a chapter on Obama.
Associated Press Writer Sam Hananel in Washington contributed to this report.