Vice presidential running mates for non-incumbent presidential candidates are, by tradition and necessity, chosen in the summer of an election year between the end of the primary season and the start of the party's national convention—unlike the other senior members of a president's administration, who are usually not revealed until the election itself is over. For this reason, the vice presidential choice is usually treated by the news media primarily as a manifestation of the presidential nominee's campaign strategy rather than as a clue about his or her approach to governing. During the "veepstakes" phase preceding the official selection, potential contenders are mostly evaluated by pundits on the basis of electoral criteria, and this line of analysis is routinely applied to the eventual choice once he or she is finally announced to the public.
Many of these strategic angles predictably recur year after year. What social groups in the mass public might a particular vice presidential candidate attract to the party? How effective are the candidate's campaign skills? Would the candidate bolster the ticket's standing in a key battleground state? Will the running mate generate excitement among the party base, or supply gravitas, or persuasively vouch for the virtues of the presidential nominee?
Presidential candidates also give careful consideration to such questions when making up their minds—since, in their view, one critical job of a running mate is to help win the presidency. Some past vice presidential selections, such as John McCain's choice of Sarah Palin in 2008, were almost entirely motivated by short-term electoral considerations; McCain was trailing in the polls and hoped that a surprise pick and a woman on the ticket would both shake up the race and help him coax disappointed Hillary Clinton supporters to cross the partisan aisle.
But little evidence exists that the identity of the running mates normally influences the preferences of voters. (Palin turned out to be a rare exception to this rule, but her unpopular candidacy backfired and ultimately benefited the opposition.) It is therefore perfectly appropriate for political analysts to interpret the VP choice as reflecting the electoral strategy of the presidential candidate, but we should be wary of suggestions that the outcome of the election itself is likely to be determined by the decision.
The running mates are much more important for the window that they provide into the presidential candidates who select them: what perceived personal limitations or weaknesses do they wish to address, and what kind of presidency might they have if elected? George W. Bush's selection of Dick Cheney in 2000 indicated that the vice president would take a major role in the policy-making and administration of the executive branch—in contrast to his father's choice of Dan Quayle in 1988, who was clearly meant to be a junior partner with little independent responsibility. Bill Clinton chose Al Gore in part to demonstrate that he would maintain a distance from the left wing of his party while in office; Gore's decision to choose Joe Lieberman eight years signaled a personal break with Clinton. Barack Obama's selection of Joe Biden reflected a perceived need to cement good working relationships with key members of Congress by choosing a Capitol Hill veteran. Mitt Romney's selection of Paul Ryan seemed designed to reassure conservatives of his ideological devotion.
Within a week or so, we'll know the identity of each party's vice presidential nominee in 2016. Plenty of media coverage will be devoted to gaming out the potential strategic implications of the running mates for the outcome of the election. But it is even more important to consider what the selections reveal about the prospective presidents who made them—in order to better inform ourselves about the choice that awaits us in the voting booth this November.