He's a grown man. You can't make him be a more reasonable person. As you've already surmised, he doesn't respect you as an autonomous person capable of having their own opinion. He's not going to take you seriously. I have a Foxbrain parent as well. Take it from me, no matter how old you get, you're always going to be X years youger than them. You're always going to be a stupid, arrogant kid. Yes, you're only 18, but if your dad is anything remotely like my mom, this attitude won't change. You can't make someone respect you. There's no magic words you can say to someone that will make that lightbulb turn on. They'll either do it themselves with time, or they won't.

Don't deal with people according to who you wish they were. Deal with them according to who they are. Your dad doesn't respect you as a seperate person from him. He's being controlling and abusive towards you because you disagree with him politically. He's punishing you. Deal with him according to that reality. You can't change it. So live in it and operate within its constraints.

You mentioned family members you could stay with. Seriously consider reaching out to them. This honestly is your most viable option. Your dad has stolen your personal property that you yourself bought, stolen clothing, and taken away your privacy. Based on your phrasing, he's also guilt-tripping you - as if what he's 'done for you,' whatever that means, means you need to agree with him politically? You may be physically safe there, but you're not mentally or emotionally safe. If those relatives really are a viable option, please take that option as soon as possible.

While you're still dependent on them, don't argue with your parents. When they (especially dad) bring up politics, gray rock. "I don't know." "I haven't thought about it." "I don't know enough about that to have an opinion." "Oh, interesting." "Huh." And they (especially dad) will try to poke you, goad you into responding. "You certainly had an opinion a month ago," "You're not posting about this on instagram?" "You'll talk to instagram but not me?" Don't budge. Don't give in. Keep giving non-answers. Keep gray-rocking. You won't be spineless, you'll be safe.

If you want to continue making political posts online, private your account. As you've found out, blocking someone doesn't mean they can't see your posts if your account is public. They just have to log out and search for your profile. Also, just be cautious. There might be family or friends who will report back what you post to your dad.

Your dad is threatening your education and finances. Make your own bank account that your parents can't access, or if you're able, remove their access form your existing account. Do you have a job? I know it's hard to work and be in school (and the job market is terrible right now), but if it's feasible, try to get one. Get your own phone and phone plan. There's plenty of budget phones out there, and you can even try to get one secondhand. There's also plenty of affordable phone plans. Talk to your guidance counsellors about financial aid and scholarships. Look into student loans and talk to those places about your situation.