When I set up the post category hierarchy originally (see the Categories box over there?), I put Mormonism under Christianity because, while it may be considered to have many serious errors according to most Christian denominations, I figured it was the best place to put it since they use the Christian Old and New Testaments (or at least their version of them) as one of their foundational scriptures. Justin Taylor, however, pointed out a New York Times opinion piece by a devout Mormon who insists that he is "emphatically not a Christian".
Now, what the writer means by "Christian" varies between a theological definition and a cultural one. Taylor deals with some of the points in the article, but then goes on to describe some of the key differences between Mormonism and historic Christianity. I think it’s a good start at understanding the religion of the likely Republican nominee for President.
And as clarification, while I think that a candidate’s religion is fair game for scrutiny during an election, it is mostly as a gauge to understand how he may act politically. I’m not electing a national pastor; I’m electing a political leader. To the degree that his religion affects his politics and policies, I think it’s worth understanding. However, this particular examination of the Mormonism is for the purposes of understanding it as a religion; disassociated from politics. Just an FYI.