I find that this hypothesis explains the observations:
It's an ideological movement. The test of support is not truth or good outcomes, but whether it fits the ideology. That's why you see some Republicans saying more and more outrageous things. They are demonstrating their loyalty to the ideology by saying things that are unacceptable from any other perspective.
I was reading some history of the Middle Ages and rise of the Enlightenment, and it reminds me a bit of that. Speaking very generally, in the Middle Ages a certain ideology ruled, facts be damned. In the Enlightenment, reason become preeminent even when it contradicted ideologies. Maybe we're headed for a new Medieval period!