That’s a good question. I think Trump prefers not to impeach because it would take away what little spotlight there is on other so “investigations” of Hitlery, Abedin, et al.
I agree with you that he will exit when it gets hotter. The assistant director really needs to go, He is real scum.
There has been about enough delay by now, and it is getting past time to clean house at these departments. This attrition thing is an albatross around the Trump agenda trying to move forward. Especially, that assistant FBI director you mentioned. As trust worthy as a cobra.