FISA judge is a part time assignment for a regular federal judge. They get this perk by being selected by the CJ, and have the perk (two week stints, a few times a year) for a term of years, IIRC, 7 years but could be 5 years. Rotation is normal. If a FISA judge was ever removed for cause, the court system would do all in its power to hide that fact.
I want to see Priestap testify in an open hearing. There has been next to no news about him and what he knows. I just wonder if he is more honest than RR and Strozk.