I just did, yesterday. As far as I'm concerned, it's not an issue. I was going there to vote, not to worship. Plus, I don't think a contemporary Lutheran church is idolatrous.
Not that I have any problem going into any sort of church for any reason other than my own worshiping. I went into Notre Dame in Paris. I went into a Catholic church for a friend's funeral.
But what of those frummer souls who feel it's forbidden to enter a church? Do they feel they have to ask a Rav? What if this is their only valid opportunity to vote?
Have any readers come across this problem? How did you resolve it? What did your posek say?