There's not really a way to prove it, since reddit doesn't have transparent moderation, but in my experience /r/politics tends to ban users with different viewpoints.
What makes you believe it then? Anyway, that sub bans people only for violent threats and such, but opposing viewpoints are downvoted a lot. They even have some pro-Trump mods on their team who can see and reverse mod actions including bans.
Anyway you can try an experiment if you care, post on there (with a new account if needed) very partisan stuff, but don't advocate for violence, and you'll find yourself not banned.