In the US, asking who someone who they're going to vote for is still taboo (at least in my opinion), they're just more likely to tell you their political stance. Plus, it's pretty easy to determine based on any number of things (do they talk about what they heard on the news last night? how do they view the current administration? government in general?).

Granted, I'm not American, but I think I've been here long enough to qualify for all intents and purposes.