Every administration effectively creates their own interpretation of what is permissible in this regard. The rules of engagement as it were that are set down by each administration vary widely. Nonetheless, it has effectively become a one-way ratchet.
I would push back against the idea that intelligence agency behavior changes administration to administration. Looking through history, it's the intelligence agencies which have superior continuity of leadership. Which suggests things about who's directing who.
Bureaucracy in general exhibits that kind of hysteresis. It is like a running average of who has been in charged mixed with a big dose of the culture that people who choose that sort of career create. Ironically, that inertia is considered by political scientists to be a safeguard for democracy.
It hits different when the bureaucracy's job is to collect and exploit secrets, and act in the shadows.
It also “hits different” when you’re the group paying for the bureaucracy.