It appears Sarah Palin (after an initial bump) may have cost (or at least strongly hurt) John McCain the election. Richard Johnston and Emily Thorson look back at the polling data.
Throughout the rest of the campaign, vote intentions were closely tied to Palin’s approval ratings: each major Palin approval drop was followed, within a day or two, by a drop in McCain vote intention. No other factor moved McCain support with such precision. Comparison of the correlation between running mate approval ratings and vote intentions from 2000 and 2004 confirms Palin’s peculiar importance in 2008.