Don't. It doesn't work. At least, facts don't work. One of the critical things we have learned from the research of Brendan Nyhan is that when we expose people who hold factually mistaken beliefs to corrections, those who are most highly informed are the most likely to dig in, and have their prior beliefs reinforced. So, if your drunken asshole uncle believes some batshit crazy conspiracy theory, exposing him to reality will only cause him to believe in it more firmly. Why? You're part of it, you conspirator, you!
People change their minds sometimes. There are tips about how to confront people with their own values, etc., but fuck that. I am a political scientist. When I am not forced to admit that, though, I tell people that I am a statistician. Why? It gets me out of having to listen to people's crap. Nobody wants to argue about statistics!
So, my advice to you for Thanksgiving, and how to deal with that drunken asshole relative, is this. Be the bigger troll! Your dumbass, redneck, racist, piece of shit uncle wants to gloat about Trump? Tell him that Jared Kushner is controlling Trump and making him a pawn of the jews! That's the great thing about racist morons. They're morons, and they get dumber the drunker they get!
And as usual, one from The Drive-By Truckers...