Karlyn Bowman and Heather Sims address that question in a column for the American Enterprise Institute website.

In May 2010, the Pew Research Center asked people if they could spontaneously name the Vice President of the United States. Although 59 percent correctly named Joe Biden, more than a third (36 percent) said they did not know. At this point, Biden had been in the job for a year and a half! This question gives us some indication of how much attention some people pay to vice presidents and how much—or how little—the choice may matter in an election.

The first rule of picking a vice president is to do no harm to the top of the ticket. But is it possible for a vice president to help a presidential campaign? Pollsters have asked questions about the choice since at least 1960 when the Roper Organization asked people whether the nomination of Democrat Lyndon Johnson or Republican Henry Cabot Lodge for the position made them feel more or less favorably toward the respective presidential candidates, John F. Kennedy and Richard Nixon. In both cases a plurality said it would make no difference, but the choice of Lodge made roughly four in ten feel more favorably toward the Nixon ticket.

Since 1980, many pollsters have asked a more political question about whether the vice presidential selection would make them more or less likely to vote for the presidential candidate or whether it would make no difference. In only a handful of the almost 60 questions asked by different pollsters since then did a majority say the VP pick would make them more likely to vote for the presidential candidate. Several of these came in 1996, after Al Gore had served in the office for nearly a full term. Over the entire span of questions since 1980, the choices of Al Gore and Jack Kemp in 1996 appear to have elicited the most positive responses. Most people usually respond that it would make no difference to their vote.