For McCain, the choice of running mate contained a wide variety of possible problems. McCain must make sure he does not alienate the social conservatives, an important element of the Republican base. At the same time, he needed someone who would not alienate the independents he needs to win. Independents are tired of seeing government distracted by non-urgent "culture war" issues and generally tired of "partisan posturing." They turned out for McCain precisely because McCain has a different brand than the Republicans. McCain has been hoping that they will forgive his general run to the Republican base as "necessary politics" while still thinking of him as a guy who will stand up to "special interests" of all varieties when elected.
With Palin, McCain opts to embrace the conservative base as the part of his coalition most in need of reassurance. The Republican big business constituency that preferred Romney has by and large accommodated itself to the thought of McCain, who has been making all the right noises on opposing regulation and corporate tax cuts. By going with Palin, McCain grabs headlines and gets folks who might otherwise have skipped watching the Republican convention to tune in.
The real question for McCain is what skeletons does Palin have in her closet and will she look credible on a national stage. The announcement of her daughter's unplanned pregnancy (but intent to keep the child and become an "honest woman" by marrying the daddy) probably doesn't do much in and of itself. What it does do is raise the uncertainty factor of how much do people really know about this person who may or may not become President of the United States. A few more surprises -- even if relatively minor -- would seriously undermine confidence in the wisdom of the choice, which would in turn raise questions as to McCain's judgment.
For the Dems, the correct tactic is not to question Palin's lack of experience, but to say that even McCain acknowledges that what is most important in a potential leader is confidence in that person's abilities and judgment. It is hard for McCain to attack Obama on lack of experience when his VP pick has even less. Since Palin must also be "ready to serve on Day 1," the argument that we have a lower standard for a VP will ring rather hollow. McCain appears to be trying to distinguish between executive experience and legislative experience. i.e., Palin can get by with less experience because, as a mayor and as a governor, she has executive experience. McCain, of course, has only legislative experience himself, so this is again something of a stretch.
I think the idea that McCain's pick will attract hard core Clinitonites is a reach. The few folks I have talked to who would fall into that category are more offended that McCain thinks they are so easily swayed than convinced to strike a blow against the glass ceiling. I suspect independent women and Dems who are attracted to this line of reasoning are more in the rationalization camp than the persuaded camp. i.e., those who say that Palin made the difference probably were voting McCain anyway.
Still, the Ds need to avoid certain rather obvious traps, while confronting a hostile media and a well tuned noise machine eager to use every device it can to whip up the conservative base to come out in huge numbers to vote. No one can ignore the fact that Dems have had a huge surge in registration and turn out this year, and despite the efforts of Republicans and talking heads in the media to try to stir up conflict in the Democratic party large numbers of Clinton supporters are following the lead of the Clintons and saying they will vote for Obama even if they are not happy about it. Given the general disenchantment of the social conservatives with the party, it is simple mathematics that the Ds will get more voters to the polls than the Rs unless the Rs can get conservative value voters to turn out in numbers at least as strong as the they did in 2004.
Making Sarah Palin a martyr to the Democrats is a decent strategy for motivating this base, even if it does not attract new voters. I expect the Obama people to bypass this trap by not confronting Palin directly, but pushing her own statements on abortion, creationism, and other conservative issues to give them the undecided independents. The Obama people demonstrated in the primary that they understand what decides elections is getting people to the polls. That was how they outmaneuvered Clinton -- by focusing all their resources on moving people to show up where they could maximize delegate count rather than trying to win huge states where Clinton had the better resources and an insurmountable advantage.
In the final analysis, McCain is still playing a desperate game in the face of serious resistance. Despite my initial response that picking Palin was a terrible move. Further analysis suggests to me it was probably a worthy gamble in a hard place -- assuming no new surprises from the candidate.