I do look forward to the gun nut Republicans' attempt to rationalize what happened without invoking anything about the gun violence problem in America.
Trump (or probably one of his people) said it's incredible that something like this could happen in this country. Of course what he means is it's incredible when it happens to him. When it happens to a kindergarten... eh, no big deal.
To be fair, and I really hate agreeing with wannabee fascist trash like Trump's entourage; it is very surprising a roof top, at most 250 yards from the stage, was not secured.
Your point still stands though, they do not give a shit about school shootings, or anyone who isn't a means to more power/money for themselves.
Coming back to this late but yeah, the security failed hard here. A bunch of bystanders got pics of this dude on the roof and tried to warn officials about him but there wasn't any response. Big failure. I still stand by my statement :)
Depends on the politics of the shooter. If left-leaning they won't waste a breath on gun violence and seize on the politics. If not...well, there's always mental illness.