I'd say the people behind the attack on Mueller are the ones that, according to the scuttlebutt now in the pipe, are going to be taken down by Mueller's work.
For that reason, I think it's rogue dems behind it. I think some dems are grey hats (Schumer & Trump cut a deal) and are just trying to play out the string until mid-terms, but a group of dems (Booker/Harris/Blumenthal group?) have too much to lose and are causing problems.
This will backfire on the dems if the lib screechers try to smear the Mueller accuser after championing CBF. Most people hate double standards regardless of political leanings, IMO. If there is a rogue dem group behind this like I think there is, then this Mueller attack means they're at the out of bullets and throwing their guns stage.