Catholicism was seen as a cult in the US up until the mid-20th century
JFKs election had a lot to do with mainstream acceptance and who could blame outsiders for thinking its strange when people say they literally ingest the body and blood of Jesus Christ every Sunday?
Opponents will be in a pickle as to how to tar Mitt with the effect of being Mormon. Implying that it makes him unacceptably “conservative” would give Mitt great joy. He wants to be thrown into that briar patch. Implying that it makes him too liberal? Naw, Democrats would never do that. Mormonism is weird? No weirder than what godless Democrats do daily.