For some of us, politics is about finding ideas we agree with and getting behind them. I think, for many others, it’s more their identity. They have an ‘other’, which solidifies their bonds with their own community. They have family and friends that are republican, and every time a lib gets owned, they get a charge of endorphins like when their favorite sports team scores.
They can’t change their mind, their political affiliation, because it’s not about ideas to them, it’s about tribalism. They’d have to abandon/be shunned by their tribe, they’d lose that closeness, that part of their identity. In addition, they’d have to admit to themselves that they were wrong for a very long time. To say you were wrong, not about an idea, but about part of your identity, is no small thing.
They’re all in. They can’t believe any other source. They remain confident because they never hear bad news from anyone they believe. They believe what they’re told by Trump and RW news sources, because not believing would mean questioning so much of their self. That’s why they won’t change their mind. I think most of those who are still Trumpers are lost, if not forever, then at least for many years. No argument CAN change their mind.