Based on what I've read in a number of venues, I venture to say that if you support Barack Obama, you may well be underestimating Sarah Palin's potential benefits to John McCain's candidacy. Here are four reasons why:
1. Many people see this choice as a pander to Hillary voters and think it won't work. I agree that the pick won't work especially well in that way. But half of the electorate doesn't like Hillary Clinton, and a solid majority of independents don't like her. A lot of people who like the idea of seeing a prominent female politician will be very happy to see someone other than Hillary Clinton play the role.
2. Attacking Palin is going to be very dangerous. A great many people will see her primarily as an amazing woman: a dedicated mother who stands by her principles and has launched an impressive career while raising a bunch of kids. This is all accurate: I think Palin's policy positions are terrifying, but I hope the Obama people are thinking very carefully about how to respect Palin's personal accomplishments as they attack her policies. Getting the tone of this wrong will seriously rile up the right-wing base.
3. A point related to #1: I see a lot of commentary assessing potential reactions to Palin based on the opinions of college-educated women. But at least initially, men like the Palin pick better than women, and to the extent that choosing Palin involves targeting ex-Hillaryites, I'll wager the swing group is the less educated, more socially conservative, more Appalachian core. I can easily imagine people from my Appalachian hometown (where my mother has long been amazed at the resistance of Democratic women to Hillary Clinton) connecting with Palin, especially if, say, Biden says something that sounds condescending and eggheaded and dismissive about her.
4. Palin's background is in journalism, specifically broadcast journalism and more specifically sports journalism. I've only seen a couple of her TV clips, but she seems to handle that environment very well, and (unlike McCain) she should be very good at reading a teleprompter, which will be important next week.
All that said, I think such a cynical, pandering, precipitous choice should ultimately hurt McCain's chances. But if Democrats think it will be easy to dismiss Palin's appeal, they could pay dearly for the mistake.