When does a cult become a religion? It seems to me to be a question akin to the one about a tree falling in the forest. There is no correct answer. Mitt Romney is a Mormon. Is he also a Christian? Is he a member of a cult? That depends on your own personal definitions. I don’t care what religion you believe in, because all of them ask you to believe in some rather strange ideas. Our country is based on the idea that no one’s religious beliefs should preclude them from serving in public office. Without any doubt, Mitt Romney is allowed to run for the position of president of the United States.
That doesn’t mean that you are obligated to ignore his religious beliefs when you make your decision on whether or not to support his candidacy. I think it would be wrong to oppose his candidacy solely because he’s a Mormon, just like it would be wrong to oppose a candidate solely because they are Jewish or Muslim or Buddhist or agnostic. But it can certainly inform your decision making.
I think it is more important to learn whether a candidate puts certain religious dogmas ahead of science. Christianity may be an established religion, unlike Mormonism, but if you reject the theories of evolution or plate tectonics because of your Christian beliefs then you are crazier than Mitt Romney, and less fit for high office.