Just the thought of appointing Bob Muller, the Obama/Clinton Uranium Bagman (while serving as Director of the FBI) to look into collusion with Russia by anyone, is mind blowing!
It isn't mind blowing to think that Rosenstein might have appointed Mueller into a somewhat protected (i.e., independent) position to provide him a modicum of cover (i.e., a shield of sorts) from claims of U1 or other improprieties.