There is the possibility the FBI campus cannot be cleansed, Huwei bugs freakin’ everywhere, fine, move our clean agents somewhere else to do their work until a safespot is built.
It certainly can't be cleansed with a derp in charge. He's probably busy rebuilding the derp infrastructure.
I can't think of another federal investigative body, though. Could the military somehow serve that function?
I believe a lot of the CIA functions have been passed off to NSA, based on Q postings.