Exactly.
Also there is no Federal law on such things. It depends solely on the state. We are allowed to discriminate for many reasons, politics being one of them. Not for race, sex, etc. etc. but politics is okay in every place I have heard of.
In what sense? Yard signs, window signs, campaigning aggressively, I understand, but what about bumper stickers, t-shirts and having Limbaugh on the radio?