I suspect the conservatives on this board have some rationale for supporting Trump, but they have not articulated it very well. It is all just some kind of grievance?

It seems to me that it's a combination of misinformation (i.e. they believe Biden isn't doing something that he should -whether or not he actually can-, or is doing something he shouldn't (which often isn't correctly reported)), and the belief that the worst Republican imaginable is still better than the best Democrat that could be conceived. As if either label is monolithic.

I remember a prominent poster at TMF. She was of the opinion that no Democrat could be worse than the best Republican (not speaking for her, but she as much as said that multiple times over the years). As near as I could tell, she just checked "D" on her ballot without doing any research. I'm sure many people vote that way, either "D" or "R". For them, it's 30 seconds marking the ballot. I'd love it if they removed the "R" and "D" from the ballots. Then people would have to pay a bit more attention (though it might not make that much difference).