Mormons belonged to a single party, the People’s Party, which was not disbanded until 1891, when the LDS leadership determined it would need Republicans and Democrats in order to persuade Congress to grant statehood. Even then local LDS leaders apparently assigned church members almost at random to join one of the two parties in roughly equal numbers.
Here is my source:
http://www.cfr.org/publication/15311/White House ... onism.html
Apparently, in the early days of the Church, leaders assigned LDS members to Republican and Democrat parties. The number was roughly 50/50.
Many members of the Church who are Democrat today come from ancestors of this initial split.
Stating that good Mormons can't be Democrat is BS. It doesn't matter which party you are affiliated with. You vote with your conscience on the issues. Sometimes they fall closer to the Republican party, sometimes closer to the Democrat party, sometimes neither.
You belong to a party so you can vote and have a say in what is happening politically.
If the early Church leaders were bold enough to actually assign members to a party, do you think they would be less bold now to tell people to switch parties?
Church leaders have not done that. They have consistently said to go and vote. They have even come out strongly on specific issues like Prop 8 in California and the ERA years ago.
Interestingly, though, the Church HAS NOT come out and said, "Don't be a Democrat."