How about this?
Dear FBI. I want to get to the bottom of this corruption.
I can’t fire Comey, but I can veto every dollar appropriated for the FBI, eliminating the entire Bureau.
Now if Comey resigned, or if the evidence showing his guilt and the guilt of the DOJ was promptly turned over, I might be persuaded to change my mind...
I think it’s even simpler than that — but I could be wrong.
Congress appropriates money. They have the power of the purse. Yes, it’s true that the president can veto spending bills, but that often gets messy.
But, as leader of the Executive Branch, I believe the president has direct control over agencies within that branch. Congress may appropriate money for the FBI, but if the chief executive refuses to spend that money ... does the bureau cease to exist?