This is the very essence of the difference that should exist between a President and a King. From Federalist 69:
The President of the United States would be liable to be impeached, tried, and, upon conviction of treason, bribery, or other high crimes or misdemeanors, removed from office; and would afterwards be liable to prosecution and punishment in the ordinary course of law. The person of the king of Great Britain is sacred and inviolable; there is no constitutional tribunal to which he is amenable; no punishment to which he can be subjected without involving the crisis of a national revolution. In this delicate and important circumstance of personal responsibility, the President of Confederated America would stand upon no better ground than a governor of New York, and upon worse ground than the governors of Maryland and Delaware.
The failure of the Republican party to support this kind of check on Presidential power is why we’re having this crisis now.
The Praetorian Guard killed some emperors, but that isn’t an official duty of the Secret Service. Of course, it wasn’t an official duty of the Praetorian Guard either.
I feel like the more likely scenario is if someone really wanted to do it, they wouldn’t, but they’d let it happen by inaction if someone else did it.
Oh shit, I didn’t see that shooter.