My understanding is it went downhill after William Webster left and the Bureau became increasingly dominated by the policies of DoJ. A lot of good career agents were squeezed out when the Bureau started implementing the same politically-correct hiring and promotion policies as other parts of the federal goverment.
I remmber at the time Clinton administration did not want to make waves with the mistery man... instead they focused on the evil white man with the NRA propensities. OKC has OBL fingerprints all over it... I guess when they saw nothing was being done why point the finger to yourself?