It is tough to comment without knowing all the variables, but a couple of things.
Is he a Democrat due to some K-urge, like loyalty to in-group? This happens to union guys who end up pledging loyalty to the group, but then the group get’s led by leftists, and they can’t bring themselves to betray the group. Here, you have to point out where the group is wrong, according to K-urges, or point out another group he owes loyalty to, to weaken his tie to the original group. That can be difficult to pull off though, if he is deep enough with the group, and if they all identify with it, if it is all they know. The NRA did this effectively during the 94 elections, getting union guys to sign on with them, and vote against the Democrats.
If you can’t identify a means by which a K-urge is holding him, then it is different. I try to see things from an evolutionary perspective, backed by what science there is. I suspect a lot of people are programmed to be highly variable, from an r/K perspective. Probably useful in history, when we would go through periodic gluts of resources, and then periodic shortages. Those adaptable to both did best over time, and passed that forward. If things go r, and resources are everywhere, these people gradually work into indulging fully, and as they do, they become less embracing/tolerant of acknowledging risk. But as things get tight, they will shift back, and learn to acknowledge risk, and deal with it in a productive manner.
As the study I quote above notes, the only way to go back towards K and Conservatism is for the risk to become unavoidable, and present to the individual a subtle threat stimuli. That is what I would try to show the Liberal. It will be a fight, because all of their drive is to try to deny the threat.
I also think getting chronically out-grouped for espousing Liberal ideas is a good way to begin this. Check the Wallace thing I linked to in the post, go to the relevant portion of the video I describe, and look at Wallace after Colonel Connell is done with him. Wallace won’t be arguing for letting American troops die anytime soon after that, whether Colonel Connell is around or not. Colonel Connell made it painful, and like a trained dog, Mike Wallace knew that was a losing proposition after that.
African American living in Philadelphia.