If you're looking ahead to the next presidential election, you can order a Palin 2012 yard sign , and the vendor may be doing brisk business in the next couple of weeks. If John McCain loses Tuesday--and maybe even if he wins-- some conservatives see her as a future president . But I wouldn't bet on it.

Palin obviously has a star quality that most politicians don't. Also working in her favor is that if Obama wins, she presents such a sharp contrast to him--down-home instead of Ivy League, feisty instead of cool, Alaska instead of Hawaii. If things go badly under a President Obama, voters will tend to look for someone very different--like when they chose the sunny, militantly anti-communist Ronald Reagan over the moralistic Jimmy Carter, who seemed weak in the face of the Soviet aggression.

But there are even more factors that will act to pull her down. One is history. If she wins and John McCain serves two terms, she'll face the difficult challenge of succeeding him--something only one incumbent vice president has done since 1836 (George Bush in 1988).

And if he loses? I can't remember the last time a losing vice presidential candidate went on to secure the presidential nomination four years later. Everyone thought Ed Muskie would do it in 1972, but he flopped. Some people thought Joe Lieberman set himself up nicely for 2004 as Al Gore's 2000 running mate. Things didn't work out that way.

Then there is the matter of Palin herself. Unlike some veep candidates who start out relatively unknown and gain ground with voters, she got the benefit of the doubt upfront and then squandered it. Right after she was chosen, 51 percent of voters had a favorable view of her. Today, 59 percent have a negative opinion.

Palin has become a deeply polarizing figure--and, more than any vice presidential candidate in memory, an object of ridicule. If McCain loses, some Republicans will put much of the blame on her and carry a grudge for years to come. And then there is that Troopergate investigation, which could still embarrass her.

All this may not hurt her with red-meat conservatives who are smitten with the former beauty queen, but they don't dominate the Republican Party. If they did, McCain wouldn't be the nominee this year. Assuming Obama wins this year, she would also probably face some serious conservative competition in 2012--starting with Mike Huckabee, who showed that an evangelical conservative could be funny, charming and unthreatening, and Mitt Romney, who has lots of fans among economic conservatives.

And there's one more thing, which could help Palin or hurt her: In four years, a lot of things can change.