To begin with, we should take a look at the list of candidates for the Republican nomination on the Campaign Status page. There are eight candidates officially in the race. A few months ago, there were several more on the table. State and national polls showed Mike Huckabee was in a strong position to win, but he declined to run. Establishment-friendly governors Mitch Daniels and Tim Pawlenty also exited the race or declined to run. Sarah Palin, who would make waves regardless of her ability to win, has apparently declined to run, though she has not made an official announcement as such. And of course, Chris Christie, who is a strong favorite to win the nomination, has not entered the race or made a convincing declaration he won't run.
If we put aside the seven candidates on the Campaign Status page who are not officially in the race, the answer becomes easier to see. Eight candidates are in the race, and only two of them have any real chance of winning the nomination. Why? Candidates are judged based on their perceived conservatism and perceived electability, which are ranked on the Candidate Profiles page. The following is the process of elimination:
There are no candidates currently in the race who possess both strong perceived conservatism and strong perceived electability. Therefore, the Republican Party's choice is to pick either a candidate with moderate perceived electability and strong perceived conservatism, or a candidate with strong perceived electability and moderate perceived conservatism. This eliminates four of the eight candidates: Michele Bachmann, Herman Cain, and Ron Paul are considered very unlikely to be able to win a general election; they have weak perceived electability. Newt Gingrich's conservatism and electability are both under question; he is moderate on both.
The remaining candidates are the electable ones (Jon Huntsman and Mitt Romney) and the conservative ones (Rick Perry and Rick Santorum). Romney has far more name recognition than Huntsman. If a voter wants someone who can win, they have little reason to shift from Romney to Huntsman. The voter may prefer Huntsman's economic record, but unless Huntsman catches fire, there's no reason to make that jump. After all, a Romney voter wouldn't want to vote for Huntsman if it would split the vote and let Perry win. Voters of a type tend to coalesce around a candidate to prevent this from happening.
As for the "conservative" type, Perry has far more name recognition than Santorum. Arguably Santorum is more conservative than Perry, but so is Bachmann. Santorum is therefore stifled in Iowa by candidates who beat him on conservatism (Bachmann and perhaps Cain), electability (Romney and perhaps Perry), and name recognition (Bachmann, Perry, Romney, Gingrich, and Ron Paul). Again, voters of a type tend to coalesce, so if you're looking for a conservative you'll go with Perry, and purists will go with Bachmann.
This leaves the race with two candidates, Romney and Perry, who lead in either electability or conservatism without sacrificing too much of the other quality. History suggests the more electable candidate will win. Perry must work hard to bring up his perceived electability and avoid taking too much damage from "pure" conservatives like Bachmann.
