Same way I deal with "know it all conservatives". Just give them facts and don't use hyperbole or fear mongering. Understand if the person is just plain stupid or has in your mind an inaccurate premise. The former just don't even bother with (both sides of the spectrum), the latter, sit down and listen to their arguments and see if their evidence does not warrant a logical conclusion to their premise.
I do not use stupid examples like "what if your wife or daughter was raped", "what if your house was invaded". Those are visceral arguments meant to use fear and emotion to make a decision.....just like our POTUS..and all of the politicians before him!