When you set up a political event, you gotta expect some unruly troublemakers to show up and cause trouble. That's what cops are for. As part of setting up the event, you get with local law enforcement, and ask 'em to show up, in uniform, and keep order. And if trouble does break out, you blame the cops for not doing their duty.
So The Donald had some sort of trouble, type and size unspecified, somewhere around Chicago, and everyone is blaming The Donald for it. I don't get it. I don't like The Donald much, and hope something happens to keep him from becoming the Republican nominee, but lets hang him for something that he done, not something that ain't his fault.
Troublemaker's showing up at an event ain't his fault. If trouble breaks out, it's the cops fault for not stopping it.