Got it.
In reverse, regarding the internal “rules” you are able to cite, it’s impossible to not want to see Sessions put a head lock on Mueller to cough up the collusion that involved Trump, alone.
Can’t bear the odds that Mueller feeds the beast toward getting Trump impeached.
Now that the public sees Rosenstein's August 2, 1027 letter to Mueller, there is public-visible justification to question Rosenstein's stepping on Sessions' toes. Sessiions didn't recuse from everything, and the DOJ regulations that Mueller is under have multiple angles to question the conduct of office of SC.
Sessions would go after Rosenstein, and reclaim cases and issues that he (Sessions) is not recused from.
I think Rosenstein has been cutting Sessions out, more broadly than he ought to. Sessions can take Rosenstien's oversight of Mueller away, and give it to, e.g., Huber. Until a case is filed in court, intra-agency turf battles are completely fluid.