There is a theory emerging, that this was leaked by the WH, in a further effort to get Sessions to resign, or if he still refuses to get the hint, to provide a fig leave for Trump firing him.
The theory being that they want Sessions gone pronto, so Trump can use a recess appointment to replace him and this avoid having to go through the Senate and a confirmation hearing. Replace him, with someone who is not recused and thus can pull the trigger on Mueller.
There are however a couple of problems with that theory. First, Mueller can only be fired for cause. Secondly, any attempt to remove him for cause can immediately be appealed to the Federal court system.
This is kind of a key part of the special counsel law; it was set up that way to make it as difficult as possible for the WH to remove any special counsel appointed to investigate him.
So while Trump and the idiots surrounding him may think they just need to reestablish control over the DoJ, the reality is that once the special counsel trigger was pulled, its pretty much entirely out of the Executive Branch’s control.