Whenever there was a major indictment it didn't really move his numbers all that much, Russia was barely even an issue in the midterms. The investigation was always more of a inside the beltway thing that cable news hyped up, I think his JA is pretty much baked in at -10 or so atp.
This is what was so bizarre about the probe. His numbers barely seemed to move after ANY of the major developments.
Remember that awful day in August of 2018 when Cohen implicated trump AND Manafort was found guilty? His numbers went.....up after it.
Voters didn't behave traditionally when following this whole saga.