No problems with the role miners play.

I'm curious if a well-funded bad actor, say a nation-state, could flood the mempool with high-fee transactions to disrupt "normal" usage.

If I understand correctly. perhaps creating many many transaction of huge file sizes (videos, high res image files, etc.). With the ill-intent of slowing down (or making prohibitively expensive) the network for all other users.

Wondering what would prevent this from happening