I don't live in the US, but here's a story from Israel: a doctor I personally know was threatened by a relative of her patient, along the lines of "if he doesn't get well, I'll kill you." She told that to the police, who asked for the relative's name, and having heard the name, told her "be careful - this guy can actually kill you."

All is well (I guess the patient recovered), but I'm not sure she'd call herself "tough enough to deal with dangerous patients without using violence"!