It has become abundantly clear that neither reason nor evidence will change anyone's political support. You can tear down their reasons, you won't change their mind. They'll just find new reasons. You can tear down the new reasons. They'll just stop listening to you, and then, in a little while, they'll forget what you said revert to their old reasons. This is true of both sides (it's why we think there are only two sides). Whatever your stance, you'll glom onto whatever events seem to qualify as evidence, and you'll investigate them only in so far as their integrity as evidence allows--like any climate denier who says "Well, it's cold today in Chicago," confusing climate with weather, which is something that has been pointed out to him numerous times but which he can't quite hold onto the next time it is cold in Chicago. You'll take in whatever feels like evidence and ignore whatever feels like counter evidence. You can't argue anyone away from his position.
What can you do?
You can move the discussion to a ground in which they have no stake, a ground where their defenses are down, where their nonpolitical hearts agree with yours. You can talk about why they believe what they believe. What are the mechanisms of belief? Everyone in his heart wants just to believe he is right but actually to be right. If the basis of their beliefs is not reason and if political affiliations are not based on evidence, where do they come from?
Two important theories explain it: the first is laid out in Thinking, Fast and Slow, by Daniel Kahneman. The other is provided by Rene Girard in The Scapegoat. For a good overview of the first, you can go here: . For the second here: and here
Accordingly, our beliefs are based overwhelmingly on our social groups, those with whom we wish to identify. Very little choice is involved. We are fundamentally mimetic creatures. The same phenomenon that makes us laugh when the crowd laughs more than when the joke is funny and makes us yawn when the leader yawns more than when we are tired makes us believe what our people believe more than what the facts dictate. We think overwhelmingly with our fast brains--which is to say with our automatic brains, the ones that say "danger, run," before ever stopping to see if the danger is real. We are mimetic creatures. We are also lazy and fearful creatures. It takes a great deal of effort to engage the slow brain, and there is a great deal at stake if we do. It may lead us away from our tribe, where we feel safe, where we feel we belong. It may lead us into uncertainty and loneliness.
But that is the task of life. And this is what you may convince the other of. This is the ground of debate. The rest is noise that elevates to violence that will need a sacrifice to quell it.
