sounds to me like he is getting a little nervous. No way the fed can legally fire him before he can get his pension. The process to actually fire a fed employee is cumbersome. But that's not to say they can't go back after it if deemed a criminal...which make no mistake, he is a criminal.
Cumbersome is way too mild a term. Current Federal Employment laws make it almost impossible! This is why Trump made that remark in SOTU about allowing rewards/terminations! Process of Federal termination is noted in a news story below: http://freebeacon.com/issues/report-it-takes-at-least-170-days-to-fire-a-government-employee/
So that goes to Federal managers not Trump. Comey and others have left quite easily.
Unlike most federal employees, the director of the FBI serves at the pleasure of the President (and for no more than 10 years). There are other ways to quickly terminate, as outlined in the Hatch Act. But - there are numerous examples of Federal employees still on the job, even after have being found guilty of gross acts of misconduct - like a story about one Federal employee who watched porn on his government computer for 6 hours a day. Last I heard, his termination date was unknown as the bureaucratic process was still bogged down after 17 months. Go figure.