Belief is largely social. This is true for all of us, to some extent. It doesn't matter much when the social belief is "our baseball team is the best". Unfortunately, the republican worldview is afactual and hateful. That's really the bulk of it, I think. People identify with republicans, or with their neighbors that are republicans, and that's the most important thing. More important than facts or truth.

Also there's a lot of authoritarians. They want a strong in-group and an out-group to hurt.

So when someone says like "So-and-so Republican is a rapist, felon, and liar" that smashes right into the "my in-group is important, and if i reject my in-group I will die alone" part of the brain. So the facts bounce off and they write you off as an asshole.

Fixing that seems difficult. Appealing to a shared group identity can work (eg: we're all americans here and we want to make the best of our great country, together). You see this sometimes where someone hates some out-group, and then actually meets a member and spends time with them. Now that person might be part of the in-group, and things have to shift around.

The other thing that changes minds is trauma. Horrible trauma. If your house gets blown apart by a hurricane, that might be enough for you to reevaluate your world view.

Anyway, the oatmeal did a comic about belief: https://theoatmeal.com/comics/believe Here's a free book about authoritarians: https://theauthoritarians.org/