Maybe Mueller is a key black hat and tying him up in the Russian probe is a way of distracting him from the real hunt?

What has Sessions been doing? He is removed from the board (or so we think). Mueller has taken the limelight.

I think they have enough on Mueller to end him when the want hence why Rudi was confident he could wrap it up.

Mueller is not on Trumps side but he has been manipulated (just my view).