Head on down to your local church and ask them if Mormons are Christians. Comedy will ensue.
Doesn't matter what they think. If they have their heads screwed on at all, they will admit that the only thing "required" to be Christian is to believe Christ will save you. Much in the way snowboarding has taken on a sense of who is a "snowboarder" and who is not, Christianity has done the same thing.
Romney is a lot of bad things but you can pretty well rest assured he's definitely Christian.