There are rumors swirling that McCain may dump Sarah Palin as his running mate. I don't believe them. She could admit to having killed a nun when she was younger and he wouldn't throw her off the ticket…and it isn't just because the "Republican base" loves her. It's because that base doesn't like a leader who ever admits he was wrong. Amidst the dwindling hordes that defend George W. Bush, there's a strong sense that never admitting a mistake is just as good as never making one.
I don't see Democrats (usually) doing the same thing. In fact, among Democrats, it's a sign of reasonableness to back down on positions even when you think you're right. In any case, John McCain can't come out and admit he made the wrong pick without telling the world he's bad at making important decisions. To get rid of Palin now would mean engineering some way in which she withdraws from the ticket over McCain's regrets. Few would believe that and even the ones who did would think less of McCain's executive prowess, calling it a mess of his own making.
By the way: Some Republicans are trying to play the revelations about Palin's pregnant daughter as Democratic dirty politicking. Actually, the news appears to have come out because The Enquirer got wind of it and was about to publish. It's sleazy but that's what that paper does, and they do it to everyone — on a non-partisan basis. (Has anyone noticed they've run a couple of stories about the pending divorce of Laura and George W. Bush? These will probably turn out to be just as true as the stories 8-10 years ago about the pending divorce of Hillary and Bill Clinton.)