Quite frankly, I am surprised that a Mormon candidate did so well. The Mormons were chased out of many midwestern states, and now a Mormon candidate for president is poised to win in some of those states. It would appear that people are becoming more tolerant of finer theological beliefs as long as views on other social issues align.
I think a Mormon candidate was an unintentional result of the rebranding of beliefs that American politics underwent. In order to get the various Protestants and Catholics under one tent, they started calling themselves 'Christian'. There's an article by
Penn Jillette that argues that it was Roe vs Wade that served as the catalyst for the rebranding.
I assume, if it was conscious at all, including the Mormons wasn't really considered at the time. But now that they're all Christian, they have difficulty rebutting Romney's claim to the name without causing further divisions to form by the same arguments.