It takes Dan Bartlett to voice the obvious problem for Romney:
"The Mormon issue is a real problem in the South, it's a real problem in other parts of the country. But people are not going to say it. People are not going to step out and say, 'I have a problem with Romney because he's Mormon.' What they're going to say is he's a flip-flopper. ... It's a fact, it's reality. I don't know if it's one that will keep him from becoming the nominee for the party but it's something they clearly understand they've got to deal with."
I have a feeling that if Romney were not a Mormon, Fred Thompson would not have a campaign (assuming you concede he has one in the first place).