The South is the weakest region for Romney, the presumed front-runner in the race, according to data from the July 20-24 Gallup poll. Romney currently has the support of 12% of southern Republicans compared with 17% or more of Republicans in other regions.

Thus, Perry’s entry would be significant from a competitive standpoint, given that his regional strength matches a weakness for Romney. That stands in contrast to Giuliani, for example, whose strongest region is the East, where Romney, the former Massachusetts governor, is also strong.