It’s anecdotal, but I personally know dozens of people that have told me they have been cut-off, unfriended and otherwise shunned on social-media and in the real world because of different political beliefs. That is, by definition, cultish behavior. - jp1692
Yeah, that is pretty cultish behavior. That being said, it still isn't the institutionalized shunning seen in JWs, Scientology, etc.. Political leaders aren't demanding that their followers cut off association with members of the opposite party/candidate under penalty of shunning; the people doing the shunning are doing it of their own accord.