Trump Campaign Press Release - Statement Regarding Chicago Rally Security Concerns
Commander George Devereux of the CPD was informed of everything before it happened. Likewise, Secret Service and private security firms were consulted and totally involved.
We have received great credit from everyone for cancelling this event. Nobody was injured and crowds disbanded quickly and peacefully. It has been termed "really good management and leadership under great pressure!"
It would have been easier for Mr. Trump to have spoken, but he decided, in the interest of everyone's safety, to postpone the event.
Donald J. Trump, Trump Campaign Press Release - Statement Regarding Chicago Rally Security Concerns Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/314598