As long as the Republican 2012 presidential field has multiple candidates, it might be hard to choose a clear-cut front-runner. But what happens as the options narrow? Philip Klein explores that topic for the Washington Examiner‘s “Beltway Confidential.”

One of the key things to think about when handicapping a presidential nomination battle is not just who is ahead at the moment, but who is most likely to benefit once the field inevitably narrows down and key Republicans begin making endorsements. On that score, Texas Gov. Rick Perry would seem to be a huge threat to Mitt Romney.

If Rep. Michele Bachmann, R-Minn., is forced to drop out at one point in the race, it seems clear that Perry would be in the better position to pick up support among her Tea Party/social conservative constituency than Romney. You can make arguments both ways for where Herman Cain and Rick Santorum (both of whom endorsed Romney in 2008) supporters may go. But none of those candidates, or Newt Gingrich or Jon Huntsman, have deep enough support to make a huge difference when exiting the race. …

… It’s actually hard to see where Romney picks up votes if it becomes a Perry vs. Romney race. So that would seem to provide Romney with two hopes of winning. One is that Bachmann and Perry get battered by the media, and by the time the primaries heat up, neither of them looks like they could be electable against President Obama. Or, Bachmann wins Iowa and stays in the race as long as possible — even better, Palin enters the race too — and splits the conservative vote, allowing Romney to squeak through as McCain did in 2008.