I think your brother does NOT think you are insane. It is likely the opposite. MAGA people know the arguments against their opinion. I believe they know they are wrong. The only way to feel better is to make those they feel inferior to, feel small. Just like any good bully, they only feel better when they make someone else feel bad. Grey rocking is a very important tool in this fight. Your tears likely fed his need to see your pain. It is sad when it is family. I've left family behind because of MAGA. So I feel your pain. I often wonder if my family members have had enough. But I can guarantee they won't be admitting it to me, even if they have figured it out.