Let's apply some intelligence to the matter, let's apply the Catholic principle of subsidiarity before lynching Trump.

Why did the local police chief not provide greater segmentation between the factions?
Why did he (maybe it was a she) not stronger crowd control and dispersion measures?
Why did the mayor know and when did he (or is it a she) know it.

and what about the Democratic (and want to be the presidential candidate) governor do?

I think the democrats benefit from such incidents. 

I think we need to look at the comm traffic between the police chief, the mayor and the governor before trying to tar and feather Trump.