Even worse is that it may be too painful for them to accept that they were wrong about something important (e.g. supporting Trump and co) and the internal conflict would likely worsen their mental health.

This is a really good point. I think there is a well-known phenomenon that demonstrates that the more people are presented with evidence that contradicts their closely held belief, they double down even harder.

And then there is the pain from all the cognitive dissonance. It’s not likely to be a very healthy state of mind.