A cult can claim what it wants to, but Christianity from Catholics to Baptists, from Orthodox to Methodists, and so on, all agree that Mormonism is not a Christian religion.
Romney is a very high, very powerful Mormon leader, that will rise even higher after this presidential effort, which by the way, is coordinated with a multi-million dollar publicity and recruiting effort from the Bishops religion, the presidential effort itself was approved by their Holy Prophet, this is historical stuff, and it is natural that this is important to Christians and literally all Americans.
So don’t vote for him if you believe he is part of a Mormon conspiracy to take over the country. Personaly, I am not threatened by Mormons. I have worked and associated with them in the military and in the Foreign Service. They are decent, family oriented people who try to live by the Golden Rule. In sum, they are a force for good in this world.