There's no benefit to cutting contact as a matter of principle. It won't impede Trump even a little and it probably won't change your dad's political views either. Is he willing to avoid talking to you about politics? Do you enjoy his company when he isn't talking about politics? If the answers to these questions are "yes" then I see no good reason to hurt him and yourself by cutting contact.
I think that every two people in my family have serious disagreements about some issue, but the world wouldn't become a better place if we all argued and then stopped talking to each other.
It's trolling. That's not to say there aren't people who seriously want this, but even those people are putting up this sign primarily to harvest the liberal tears.