Tell them that anybody who talks politics does not get dessert or anything else to eat.
Mine is a little easier, being the only Sci-Fi geek in the family, I just start in on Doctor Who, Captain Kirk, Star Wars or The Hitchhikers Guide To The Galaxy, and they start looking for a dog for me to walk
Don’t invite them.
You could always lead with: How about those Nationals? (Or Blues…)
I just bring out my banjo; which results in mucho screams and “Please don’t’s”. I then just sit the rest of the evening with the “banjo on my knee”. The fear of the sound of a banjo immediately squelches any argumentative subjects at the dinner table.