Okay you've known them for years. That's a large time investment.

So when they do something you disagree with at a fundamental level, ask them to explain oh why do you support that? And then when they give you a high level answer ask them why that is there answer. Like peel the onion to get to their core issues. And if people's core issues that's just what other people say and they haven't thought about it, you're going to help them think about it for themselves. Which may not convert them but will at least get them to apply some intellectual rigor to their thinking