I get being weary of a dog that is coming at you at a reasonable speed... but to go from that to drawing a gun and shooting it ? Don't cops have a baton or similar blunt melee weapons he could use to shield himself in case the dog was actually hostile ? The wasn't even showing any signs of aggressive behaviour from what I could see in the video.

Are cops nowadays not trained in anything except drawing and shooting ? Did the bar to which an officer can start carrying a gun lower so much that any idiot who can draw and shoot is given a badge.

I'm neither an American or a dog owner and this video still looks like insane amounts of incompetence to me. I've never met a dog that is particularly cunning in disguising that he is going to attack you, almost all of them signal pretty clearly, baring their fangs, growling, body position and barking.