Leaving aside any of her merits and demerits as a candidate for the office of Vice-President, I’d say that opponents of the McCain ticket would be wise to steer a million miles clear of her daughter’s pregnancy, as Obama already has done.
A lot of Bush opponents thought that hammering the guy as an alcoholic or raising questions about his possible past drug use would hurt him, or for that matter pointing out that he was an indifferent frat-boy student who largely maintained that posture into adulthood would hurt him. The thing of it is, much of that endeared him to people who could identify a lot more with that personal history than they could with his opponents, and the way Bush has chosen to acknowledge (if not openly discuss) that history has also been very strongly reconciled to evangelical narratives about sin and salvation.
There are a lot of reasons to think Palin is not a good candidate to be a heartbeat away from being President. But this is a part of her story that can very easily resonate with a lot of “Red America”. Remember that many of the discrete issues that social conservatives campaign about in public are actually much more acute and common experiences in communities that skew strongly to religious or social conservatism in their voting patterns. An educated upper-middle-class professional family can have a teenager who is pregnant, too, but that becomes more common in lower-income communities for a whole range of reasons. There are other complicating social cleavages, certainly: race skews voting patterns in different directions even among communities where teenage pregnancy is a bigger issue. But opponents of the McCain-Palin ticket would be smart to avoid appearing smug or superior about the whole matter.