While I agree that this is not Trump's fault - directly anyway - I do think he has been courting disaster with the tone he has set. His constant rhetoric and fear mongering is designed to whip his supporters into a frenzy.
Just compare what he says and does to McCain's reaction to the same fringe elements.
We have never had a national politician so focused on feeding red meat to his base. Every other president has at least paid lip service to being the president of everyone.
Trump has put this country on a path that made something like this pretty much inevitable. I doubt it would have happened without him. We will see.