Political identification bias
Political identification bias describes the tendency to make blind guesses or assumptions about a person's political affiliation based on whether or not we agree with or like them.
Sometimes, a person may base the guess on things they usually associate with liberals or conservatives. For example, we might assume that a gun owner who goes to church is a conservative while we might assume that an atheist is a liberal. More often, however, we make such guesses without knowing much or anything about a person's opinions.