Lest anyone get the idea that the FBI is lax on tracking spies in this country (and they are still here and still faithful to mother Russia as well as many other countries and ideologies, the Director of National Security uses a different section of the FBI for security matters.
This does not mean there should not be an investigation of the FBI after this is all done. The actions of what may be only a few have called into question the integrity of everyone, and the only way to get any reassurance is for both internal and independent investigations to take place.