I think taking a position of "backing" a huge group of people comes at the cost of holding them accountable. You can't "back the FBI" and then turnaround and say that some of them should be fired. And certainly there are people in the FBI, not connected to the Trump situation, who have done shit they should be fired for.
Saying "I support the FBI," especially right now, implies that regardless of the situation, regardless of the actions, you have picked the people you are supporting, frequently against another group of people, regardless of the particulars of the situation. I save that kind of backing for family, and even that has limits.
I support laws. I support the objective, fair enforcement of those laws. That includes the laws that limit the FBI.
To me, the "If they can do it him, they can do it to anybody" is great insight into the Republican mindset regarding criminal justice. You don't see Republicans saying that about victims of police violence, like Breonna Taylor or George Floyd. Because they know it's not true. There is a social hierarchy, and they see black and poor people near the bottom of that hierarchy. Their major defense comes down to why Taylor and Floyd should be subject to the violence - Floyd with his past criminal issues and Taylor because she once dated someone a criminal. It's okay if the police victimize folks lower down, because they wouldn't dare do it to a middle class white guy. But with Trump, their concern is the cops are going after a rich white guy. That's a fear the GOP can exploit. If they go after Trump, then no one is safe. To them, the disproportionate impact of police violence is what makes it acceptable, or even desired.