For many decades it has been the unwritten law in DC that one does not go after former political leaders.
Why so others don’t come after you when you leave.
Unless your a republican and are trying to clean up government then the big guns come out.
I agree that politicians rarely went after former politicians and high level bureaucrats for exactly the reasons you stated. They want protected themselves. The media is now politically aligned so they cover up for the crooks. It is why corruption is running rampant and it is hidden.