Romney's prospects can't be fully assessed without coming to grips with this fact: Most Americans are affiliated with churches that — notwithstanding important differences among Catholics, mainline Protestants and evangelical Protestants — stand in the same line of historic or traditional Christianity. The Church of Jesus Christ of Latter-day Saints, as its most articulate representatives will tell you, stands apart from that line.

Mormonism says that the early church fell away from the truth and withered for roughly 17 centuries and that "in the latter days" Christ has been restoring his church. He has done so through living prophets in receipt of continuous revelation that becomes scripture and may guide interpretation of the Bible. Historic Christianity does not accept Mormonism's belief in the necessity of a restored church; or its understanding of modern prophets and continuous revelation; or its acceptance of an open canon of scripture, which for Mormons includes the Bible, the Book of Mormon, Doctrine and Covenants, and Pearl of Great Price.

There are more differences: Mormonism says that God has a material body and that he had a beginning in time, having himself been fathered by another God, but historic Christianity (and Judaism, too) says that God is a spirit and that there is none before him or after him — that he is eternal. Mormonism says that God created the universe out of existing matter, while historic Christianity (and Judaism, too) says that creation was ex nihilo. Mormonism says that God fathered every human being — we lived with him in "the pre-existence" before our sojourn here on Earth. Mormonism thus believes that God and man are ontologically the same — the same species, if you will.

But historic Christianity (and Judaism) maintains a sharp distinction between God and man. Regarding man's destiny, Mormonism says that man may become (in Joseph Smith's statement) "what God is," a phrase that would seem to encompass all of God's attributes, but historic Christianity says that by grace man may become not God but like God and that by no means will man acquire God's "incommunicable" attributes, such as omniscience and omnipotence.

Protestants and Catholics who are serious about their Christian faith are likely to see Mormonism as heretical in key respects, even non-Christian. The historian and scholar of Mormonism Jan Shipps has described it as not a part of traditional Christianity as such but "a new religious tradition." Would such perceptions of Mormonism lead voters to decide they couldn't vote for Romney?