I am truely disappointed in you for the way you posted this.
Up to this point the "discussion" and "focus" has been on cops that shoot pets immediately on encountering them - usually in the context of a dynamic entry no-knock search warrant being served. Almost all of the dogs shot in those circumstances were not actually attacking the sudden intruders into their territory - merely announcing that "This is my house, not yours. Get out now before I do start opening up a can of whoop-azz." Also, many of the dogs being shot are of the smaller breeds - not saying they cannot inflict injury but the liklihood of them ripping out your throat or guts was fairly small.
Now we get a dog that does not, from the description of its behavior, merely announce you are on his turff. It actively put the cop in a good position for the killing attack.
The cop committed a vast number of stupid moves, but none of them negate the fact that his life was more likely in danger than most of the door-busters we usually read about.
I'd like to turn this into a SD teaching moment by focusing on the fact that the cop shot the dog only one time. It was a "one shot stop" in that the attack was stopped - even if the dog did not go down DRT. I'm willing to bet that the cop kept his eye on the dog after he shot it and the attack stopped. But I'm also willing to bet the cop was not scanning the area for other threats or to locate other cops who might be in the area and responding to the gunfire. It's hard to remember to do all that when you are puckered up past 11 on the dial, but it sure does help keep you safer if you can do most of those things.
stay safe.