Until the past week, Trump also faced isolated individual protesters. I think he bears part of the responsibility for the loss of civility through the way he handled those individuals. And no, I am not excusing the behavior of the mobs who are ruining his rallies. But, the BLM people and the Bernie supporters have an excuse to push back that they wouldn’t have had if Trump had acted differently.
The individuals that protested Trump prior to Chicago clearly went out of their way to sabotage his speeches and malign his supporters. They did not go there to engage in policy discussion at a meet-and-greet venue, for example, as they had did with Cruz.
If Cruz is nominated, his "brilliant" discussion on policies will be no match for the hundreds of BLM mobs and agitators that will reign down on his rallies.