In the end, I think the core duties of the FBI will be split up. The DOJ might be able to retain one-third of what is the FBI today, but I think the rest will split off to some other creation. It’ll probably happen after Trump wins 2020, and the Senate has a 60-plus GOP control situation.
The FBI has been corrupt in the sense of being politically biased and acting on its bias for years and really reached peak corruption under Obama. But leaving aside the recent stuff, even starting with Hoover (who was a political fanatic in the opposite direction), its tactics have been of dubious constitutionality and even of dubious legality: blackmail, anyone? or perhaps you’d prefer an agent provocateur.
It needs to have its legitimate investigatory duties spun off, say to the DOJ, and its other powers handed over to the US Marshalls or some other established and non-political law enforcement agency.