You gotta wonder about that FBI

Jeff Sessions just fired the FBI's number two man, Antony McCabe, based upon the FBI inspector general's written recommendation.  Just to make it hurt a little more, McCabe was within hours of retirement, with a full pension.  Getting fired means no pension, a pretty harsh penalty. 
   Question, if McCabe was such a crumb bum, how did he rise so far in the FBI?  I assume McCabe joined the FBI twenty years ago as a junior agent, or what ever the FBI calls new troops.  Since over twenty years, he got himself promoted up to number two at the Bureau, he must have had a lot of supervisors writing good performance reports on him over the years.  Is it a case of a good guy turning bad in his later years? Or is it case of a lot of McCabe's supervisors thinking McCabe's way of doing things was good?  That in fact a lot of the Bureau's supervision is just like McCabe?  And that maybe some more weeding out is in order?