Praetorians.
Yes— and they are documented by Suetonius to have settled the problem of the monster insane Caligula. But Rome was not a Constitutional Republic.
Check out the origins of the “secret” service— they came from the Pinkertons for Abe Lincoln. Pinkertons are still around commercially, and one of them got away with murdering planned murdering of a peaceful guy in Colorado who made custom cowboy hats for a living. The Pinkerton there was “working for” an NBC affiliate “reporter” but had a NBC producer on the location ready with multi camera angle record of the set up hat maker who came to a “Support the Blue” rally, of bikers and Veterans (as this victim was, a Veteran). Clearly planned and the clown Pinkerton was fully outed as to his AntiFA affiliations-— and cleared in an idiotic trial. Murder— they carry to murder.