Given all of her negatives (utter lack of experience, pending abuse-of-power probe, right-wing Christianist (aka Dominianist) convictions, profound lack of readiness to be President), McCain’s choice could have only two goals:
1. Solidify the far-right base.
2. Peel off Hillary supporters who remain on the fence, due to disappointment with the outcome of the primary.
The first is a given; the second shows such extraordinary contempt for the process by which people make these kinds of choices that I can’t imagine it will succeed (I should note that my wife is utterly furious with the presumption that women will automatically vote for another woman).
I’ve read numerous analyses of McCain’s choice today, but the most succinct and cogent so far has to be that of Jeff Fecke at Alas, a blog.