In reference to "HN users who are flagging political/US election-related topics in general"? By topics I mean submissions, not comments. I'm assuming the jokes you're referring to are in comments.

Comment flagging/up voting/down voting behavior is interesting as well, especially as I've seen discussion that voting behavior can indicate agreement (do I agree with the comment?) or substance (do I think the comment adds to the discussion?).

As for bias, I'm not ready to wade into that without more analysis of what's actually going on. It's too politically charged. I'm speculating about what I think is happening. Please don't read this as taking a position on the behavior itself.