I'm gonna assume that you've already weighed the options of cutting them out of your life, but for personal reasons have decided against it or it's not a moral option you can choose, so I won't open with the advice of 'walk away'.
Instead, I'll say that you shouldn't argue with them or try to change what they're doing unless they specifically ask you for advice. They're doing this crazy shit of their own choice, and as a friend you have to either accept that or walk away. If you want to keep the relationship between the two of you civil, focus your conversations on not discussing politics or current news. Put it on yourself, like "with all the crazy stress in the world, I don't want to talk about that stuff", or shit, be honest with them (to an extent) and say "I don't think we'll ever see eye to eye on this stuff, and you're an important friend to me, so I'd rather not talk about that sort of stuff".
If they value you as a friend, they'll respect your wishes, and if not they're either so over the cliff that you can't save them or they don't have nearly as much invested in the relationship as you do.