Well, at the moment, the most likely is Sarah Palin. But, as Parker observes, even this is not likely. And the answer to this question, naturally, goes back to the Great Male-Female Charisma Gap. Palin has some charisma, but I doubt if it’ll be enough to win a general election. And there are, it seems, precious few women who possess the charisma that is needed to win. Poor Mrs. Clinton had Nixon-esque anti-charisma.
I’ll say this, though. I think charisma is-at least partially-a genetic trait. So, I figure the most likely candidate for first female President is probably Malia Obama.