For the most part, anyone in the Executive Branch. There can be some push-back when it’s widespread in Justice or State, but it’s within the president’s powers. The main reason why Trump’s had pushback is the context of firing Comey, McCabe, and pushing out Sessions & Rosenstein and their involvement in investigating him.
The Judicial Branch is off-limits.That’s a one-way street.
Wow, they get this motivated to clean house, I bet they’d be really motivated to prosecute an FBI operative who: illegally bugged a major civil rights leader having sex, then anonymously sent the fruits of their surveillance to the person’s wife, along with a letter to the man himself urging him to kill himself.
But what do they do instead? They name the FBI Headquarters building after him.