Might be a bit simplistic
But why didn’t the police just point blank refuse to tear gas those peaceful protestors in DC?
Because The Commander In Chief told them to do it.
All my years of watching American army films has taught me one thing:-
'Americans will do as they are told, until there's the chance not following orders will result in they themselves being killed.
At that point - orders what orders...
...Aaaarrrgggghhhhhhhh - I've been shot'.