In anointing Sarah Palin as his running mate, John McCain was gambling that women voters will be more likely to vote Republican with the prospect of seeing a woman in the vice president's office. Does history bear this out?
Of course, we only have one case to look at: 1984's election, with Geraldine Ferraro as the Democrats' vice presidential nominee. Still, we can ask, was the gender gap wider in 1984? Did women cross party lines to support Ferraro? It doesn't look like it. The graph below shows the percent of men and women who voted Republican in each presidential election between 1948 and 2000:As the graph shows, the gender gap is a surprisingly recent phenomenon. It's only been occurring consistently and with any real strength since 1980. As for Ferraro, it doesn't look like she had much of an effect here. The gender gap in 1984 (7.6%) was exactly the same as it was in 1980, and was considerably smaller than it has been in recent elections.
Does this mean that Palin won't have such an effect? Hard to say with only one data point. And maybe things are different in a close election. But history still doesn't testify to much of a VP effect.