According to Gallup, Republican and Republican-leaners of voting age who identify as Mormon are disproportionately likely to support Mitt Romney, while Ron Paul garners more support among atheist Republicans than he does among Republicans of all religious denominations. Romney collects 71 percent of the Mormon Republican vote, exceeding the 23 percent he scores among all Republicans, and Paul garners 19 percent of the atheist vote, more than the 10 percent of all Republicans who support him. Gallup surmises that Paul's support among atheist Republicans at least partly reflects "the youthful skew in Paul's support and the tendency for young Americans to have no formal religious identity."
But Republican voters do not always support the candidate who shares their religious denomination: "Catholic Republicans were no more likely than average to support the two Catholics in the GOP race, Newt Gingrich and Rick Santorum; Protestant Republicans did not disproportionately support any particular candidate." 26 percent of Republicans who identify as Catholic support Gingrich, less than the 28 percent of all Republicans who support him. And four percent support Santorum, only slightly more than the three percent of all Republicans who support him.

Similar to Catholic Republicans, Protestant Republicans "reflect the overall sample average in their candidate support." The three major Protestant candidates are Ron Paul, Rick Perry, and Michele Bachmann (who has just suspended her campaign). Paul only gets 10 percent of the Protestant vote, which matches his score among all Republicans; Perry gets eight percent of the Protestant vote, only one more percentage point than his support among all Republicans; and Bachmann scores seven percent of the Protestant vote, just surpassing the six percent of all Republicans who support her.
Although Romney attracts the vast majority of the Mormon Republican vote, Mormons represent a relatively small percentage of the voting population. Gallup writes: "Given that Mormons constitute about 2% of American adults and 4% of Republicans nationally, the more important factor may be any possible effect that Romney's faith has on the vote of highly religious non-Mormons, a much larger voting bloc. The current data show that highly religious Protestants do give Romney slightly lower support than he gets among all Republicans, although the five-point difference is not huge."