Editor's note: Dan Schnur is the director of the Jesse M. Unruh Institute of Politics at the University of Southern California. He served as the national communications director for Sen. John McCain's 2000 presidential campaign.
(CNN) -- If you agree that a presidential nominee comes to the selection of his running mate the same way a football coach develops strategy for the last few minutes of an important game, then Rob Portman and Tim Pawlenty are the political equivalents of running your fullback off-tackle.
There's little risk associated with either choice: Both keep you moving slowly but surely in the right direction. So it's no accident that as the polls stay close, speculation surrounding Mitt Romney's vice presidential nominee has focused on these two eminently qualified but exceedingly cautious alternatives.
Earlier this year, when Romney trailed in the polls by wide margins, the strategic calculus was entirely different. When your team is behind by a couple of touchdowns, you put the ball in the air. It's worth risking an interception if you need to do something dramatic to change the course of the game quickly. The difference between Dick Cheney and Joe Biden on one hand, and John Edwards and Sarah Palin on the other, is the difference between a presidential candidate who thinks he's going to win and a candidate who's worried that he's going to lose. Confident nominees make safe choices. When they get nervous, they start taking chances.
So it's not surprising that discussion about options like Florida Sen. Marco Rubio and New Jersey Gov. Chris Christie has diminished in recent weeks. Both are highly respected public officials, but both represent the equivalent of telling your quarterback to start throwing long. Rubio and Christie aren't desperation passes by any means, but both would represent a much more aggressive and potentially risky approach to the campaign than would a more conventional choice like Portmann, a senator from Ohio, or Pawlenty, former Minnesota governor.
The question is how confident Romney and his advisers feel about the campaign's overall trajectory. They've been taking a beating for the last week or so as Team Obama unloads with attacks on Romney's tax returns, professional biography and investment portfolio. But it's not yet clear whether this barrage will cause any lasting damage.
By the time Romney returns from his foreign travel next week, it will be easier to tell whether he can continue to keep the ball on the ground or whether it's necessary to reframe the race. If the Bain assaults are having an effect, then even a short-and-medium range passing game might become necessary. At which point, names like Rubio and Louisiana Gov. Bobby Jindal will begin to surface.
Christie, unfortunately, seems to be an even less likely selection at this point. The more Romney aides talk about the importance of personal compatibility between their candidate and his running mate, the odds of the Springsteen-quoting, union-bashing, china-breaking Christie making the cut seem to diminish significantly.
Nominees will always tell you that the ability to govern is the most important quality they look for in a running mate. But there are a lot of qualified people out there; the tie-breaker is almost always what the polls are showing.
Various college football coaches from a previous era, most notably Ohio State's Woody Hayes and Texas' Darrell Royal, are credited with a saying about the relative benefits of running the ball. "When you throw a pass three things can happen to it, and two of them are bad." Any number of modern-day quarterbacks, from Aaron Rodgers to Peyton Manning to Tom Brady, would argue that a more aggressive approach is not only preferable but necessary. Romney's most important decision as a presidential candidate will be to decide whether it is more dangerous to be risky or risk-averse.
Romney's natural inclination has always been to follow the more cautious path, which increases the likelihood of a Portman-esque selection. We'll see in a couple of weeks whether he and his campaign team believe they have the luxury of playing it safe.
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The opinions expressed in this commentary are solely those of Dan Schnur.