While pundits breathlessly speculate over Mitt Romney’s choice for vice president, it’s worth noting the extent to which — regardless of who he chooses — it won’t be a “game changer.” Both Rob Portman and Tim Pawlenty, the top picks for the vice presidential nod, come from states in Obama’s coalition that are vulnerable to a GOP pickup. Portman is the junior senator from Ohio, a swing state which would almost certainly form the basis of a winning Romney coalition. Pawlenty, on the other hand, is the former governor of Minnesota, a blue state which — if the national economy were to deteriorate — could become competitive, on account of its large population of working-class whites.

It’s true that the simple act of choosing a vice presidential nominee can provide a boost in the polls. From 1984 to 2008, presidential nominees received a median bump of 4 points after choosing a vice president. But this bump almost always subsides, and the polls return to their pre-choice status quo. A presidential nominee might hope that their choice would deliver votes in November, but available evidence shows that Veep candidates genearlly have little impact. On average since 1920, the vice presidential choice has produced a net gain of only 2.2 percentage points for the top of the ticket — in his home state.

In a close election, this could mean the difference between winning and losing the presidency. Indeed, given the close forecasts for this election, a net gain of 2.2 points in Ohio could determine the presidential contest. But even that outcome is less likely than it seems. In Ohio, Obama’s margin is large enough such that a 2.2 swing would turn the race into a genuine toss-up. In other words, there’s little chance that the vice presidential choice will prove decisive.

None of this is to say that we can’t learn anything from who Mitt Romney chooses as his running mate. Presidential nominees ought to look for competence and experience when choosing a vice president. If Romney bends to pressure and goes for an “exciting” pick — like first-term Florida Senator Marco Rubio — he might undermine his persona as a competent manager. His short­list — Pawlenty and Portman — is also a sure bet for choosing the optimal running mate—competent, inoffensive, and ready to govern in event of an emergency. But in political terms, Americans generally cast their vote for the top of the ticket. The rare occasion where the Veep candidate matters, i.e. Sarah Palin, is the exception that proves the rule.

Jamelle Bouie is a Writing Fellow at The American Prospect. You can find his blog here.