I snipped & bolded part of your post.
I think that's what the most stunning piece of this is -- almost anyone would have said that the Secret Service should have ensured that roof/building was secure. Anybody who has ever watched a movie or tv show that depicted the Secret Service or even anything with bodyguards would have easily known that.
The level of incompetence is shocking.
The shooter was literally in the best shooting position possible. Really is shocking for sure.