"To me it's an expression of principle, Truman saying that it doesn't matter whether or not the blame can be pinned on him for some specific problem, but rather that as President he is morally responsible for everything that happens everywhere in the government. He's rejecting not just fingerpointing, but specifically the kind of fingerpointing in which a subordinate is thrown to the wolves to protect the President."

Well, if Truman thought he was morally responsible for everything that happens everywhere in the govt. I don't want this guy as President.
I want a President who doesn't think he controls everything. I want a human being as President not so someone who thinks he/she is God.

I think Truman was stating the obvious. Human being are unwilling to accept responsiblity as a general rule- therefore one thing humans do is pass the buck. So passing the buck is typical and it ends up at the President or any other leader [CEO or captain of a ship]. "Morally responsible for everything that happens", is about as the same as "I feel your pain". I want a President that is morally responsibility for his/her actions [and he/she can work on being God on his/her own time]. And want a President that can feel his/her own *pain*- so the idiot might possibly stop doing stupid things [like getting blowjobs in the Oval office].
Now being responsible for your actions does not just mean what is done overtly by you, it also means what you allow to happen [when it's within your power to do something about [which tricky thing to be judged about, e.g. what do you do if someone is being robbed or attacked in front of your eyes or what do you do if you think your plane is being highjacked by terrorist who are probably going to use your plane as a weapon. Maybe you are just nervous wreck and are physically incapable of doing anything- whereas some people prepared and are practiced or it's "natural for them" to be able to respond, but may fail to act for other reasons, etc].
Now, what some people are accusing the President of doing is allowing someone who is incapable of handling an emergency be in charge of handling a emergency. Now, if a person is being visciously slandered by media circus, an valid option is to remove this person. This isn't throwing someone to the wolves. Rather it's the wolves are making that person's job impossible to do.