The reverse presidential race is entering its critical phase with a handful of GOP candidates presumably pondering how long it is worth it to uphold their more or less futile attempts of becoming popular enough among the right-wing constituency. Which of the more well known candidates is going to fold first?

An LA Times commentary on the subject:

"Will he [Santorum] be the next GOP campaign dropout? Santorum finished fourth at Ames, worse even than Pawlenty, who said he needed a strong showing to maintain sufficient donor interest. The Minnesotan didn't get it and pulled the plug the next day on his substantial Iowa ground operation.
But Santorum had much less invested in Iowa, other than miles and time. And fourth place for him seemed better than expected. So he postponed his return to Pennsylvania and went to the Waterloo dinner to continue his quiet guerrilla struggle for support as a conservative alternative to Mitt Romney in hopes that Perry and Bachmann somehow knock each other off.
Santorum pecks away at Bachmann much as Pawlenty did, for her alleged lack of congressional accomplishments, and at Perry for his seemingly diffident same-sex marriage stance.
Or what about Herman Cain, the pizza godfather? Probably not, not yet anyway.

Gallup compiles what it calls a Positive Intensity Score, a measure of a candidate's strength of support. Although he regularly polls down in the pack, Cain's intensity is the highest among Republicans, 25. Next already is Perry's at 23 followed by Bachmann at 20 and usual poll leader and top moneyraiser Romney stuck at 15. The undeclared Sarah Palin also has 15 and Rudy Giuliani has 20.
Ron Paul finished a close second at Ames and his devoted disciples wouldn't let him quit even if he was discouraged by his disappointing intensity score of 11.
According to the same score, the weakest remaining GOP candidate now is Newt Gingrich at only three. But his debate appearances help his other business, selling books, DVDs and maintaining his speaking fees.
Jon Huntsman's intensity score is only four and Santorum's isn't much better at six. So, watch for one of them to fade, especially if Santorum's fundraising stalls back home." http://latimesblogs.latimes.com/washington/2011/08/rick-santorum-newt-gingrich-rick-perry-michele-bachmann.html

Gallup's "Positive Intensity Scores": http://bit.ly/nK5f73