I don’t know that you can blame Trump directly for the violence, but you cannot completely absolve him or his supporters, either. When you have a Trump supporter sucker punching a protester, and then saying the next time he might have to kill him, and Trump supporters CHEER him; when you have Trump supporters roughing up protesters and you have the candidate approving and even offering to pay the legal bills for anyone arrested for attacking a protester; when you have Trump himself threatening to punch a protested in the face from the stage during a rally; then yes, I think you can safely say that the Trump campaign and many of his supporters share some of the blame for the potential for violence.
Ted Cruz is a sad POS for blaming Trump for a bunch of left wing protesters. He is going to lose badly thank God.