Which Sarah Palin will viewers see tomorrow night?

Will she be the feisty and self-confident Sarah Palin of early September, or will she take on that moose-caught-in-the headlights look of her interview with CBS News' Katie Couric?

Tomorrow's highly anticipated vice-presidential debate at Washington University in St. Louis carries real risks for both parties' candidates, but the stakes seem particularly high for the Alaska governor, who has spent the past three days at Sen. John McCain's Arizona ranch, cramming for tomorrow's encounter.

In the past two weeks, the Republican nominee for vice president has received scathing reviews for her hesitant performance with Ms. Couric and in other interviews. She has seen her favorability ratings slip and been criticized by some conservative columnists who consider her a liability to the GOP ticket.

Her Democratic opponent, Sen. Joseph R. Biden Jr., has had his own share of missteps on the campaign trail -- you can view a "Biden Gaffe Clock" at www.GOP.com -- and the Delaware senator, long known for running his mouth before he sticks his foot in it, has a team of "minders" assigned to keep him on the straight and narrow.

Still, the Obama campaign hasn't done too much to rein in Mr. Biden, even after his recent claim that Mr. Obama was against "clean coal." That remark triggered three ads in recent days -- two from McCain mocking Mr. Biden and one from Mr. Obama, reiterating his support for the coal industry.

Ms. Palin has come under fire in the past week from syndicated columnists Kathleen Parker and George Will and the New York Times' David Brooks about her readiness to be vice president, but talk of a full-fledged backlash against her is overblown, GOP operatives say.

"I don't know too many people other than those on Grant Street who read David Brooks," said Robert Gleason, chairman of the Republican Party of Pennsylvania. "I think Sarah Palin has captured America's interest. Not their support, but their interest. They're not attracted by her knowledge of foreign affairs, but by the fact that she's an accomplished woman with five children, one of whom is disabled. I think Democrats are in denial about her."

Indeed, Ms. Palin's problems in the Couric interview were less about substance and more about tone. "She seemed defensive and over-prepared," said Daniel Schnur, director of the Jesse Unruh Institute of Politics at the University of Southern California, who worked for Mr. McCain's 2000 campaign.

Nonetheless, those expecting a faltering performance from Ms. Palin should not underestimate her, said Judith Bendersky, an Anchorage, Alaska, resident who attended several debates featuring Ms. Palin during the 2006 gubernatorial contest.

"She is a very bright, capable person, and she is boning up on the topics and is a fast study when she has to be," said Ms. Bendersky, who is not a political expert but characterizes herself as politically active.

During a series of political forums around Alaska, Ms. Palin "handled herself beautifully. She came off with great aplomb against more knowledgeable people armed with lots of statistics and facts and experience. Debaters should beware her gifts and charisma."

But in recent weeks, the spontaneity and freshness that brought such a lift to the McCain ticket seem to have vanished, "due to too much micromanaging by McCain's handlers," said Douglas Brinkley, a presidential historian and Rice University history professor.

"We've seen two Sarah Palins since the Republican convention: One was someone who spoke from her heart -- a real superstar; the other spoke from her head, and sounded like an imbecile. The Republicans have been filling her up with too much information, too much of 'don't say this, don't say that,' and I think that's unnerved her," Mr. Brinkley said.

"If she talks about being a mother, being a wage earner, who understands and relates to real people, she will be fine. If not, she could become another Admiral Stockdale," he said, in reference to independent candidate Ross Perot's running mate, whose 1992 debate performance helped sink Mr. Perot's candidacy.

For his part, Mr. Biden will focus less on Ms. Palin than on the man at the top of the Republican ticket, said Allison Price, an Obama campaign spokeswoman. "Joe Biden, like Barack Obama, will be a fierce advocate for the middle class, and use this debate to talk about the change we need on the economy, health care and energy independence," said Ms. Price.

"I think Joe will be cautious and will respond to questions as best he can," predicted Mr. Gleason of the Pennsylvania GOP. "I would be surprised if he tried any tricks or made her look bad.

"And I think she will approach it in a similar fashion, and address the questions as best she can. ... I'm not so sure that either one of them will try to prove anything in this debate, because vice-presidential debates don't sway the outcome of the election," he said.

Although neither candidate is viewed favorably by a majority of Americans, according to a new poll by the Marist College Institute for Public Opinion in Poughkeepsie, N.Y., voters give the edge to Mr. Biden in tomorrow night's debate.

While 61 percent of those surveyed said Mr. Biden would have a better grasp of issues, compared with 23 percent for Ms. Palin, those low expectations could be a plus -- a factor Mr. Obama's aides have recognized. Over the weekend, Obama campaign manager David Plouffe called Ms. Palin a "gifted debater."

"Clearly, the bar is set a little higher for Senator Biden because more people expect him to do well," said Lee Miringoff, director of the Marist College poll. Additionally, the financial meltdown on Wall Street and Monday's rejection of a bailout bill in Congress will inject an unusual note of drama into the debate, the only one for the vice-presidential candidates.

"It's an opportunity for the national ticket to use the vice-presidential candidates as spokespeople for them on the financial crisis," Mr. Miringoff said.. "The role they'll be performing is more than just, 'I'm qualified to be president in the event of an emergency and here's why.' They will each have to act as a mouthpiece for the presidential candidates on this critical issue, and that's very unusual."