A police officer attempts to calm an attendee after the cancellation announcement of a campaign event with Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, at the University of Illinois at Chicago Pavilion in Chicago, Illinois, U.S., on Friday, March 11, 2016. Trump canceled a Friday evening rally in Chicago after his campaign met with law enforcement and concluded it wasn't safe to proceed amid extensive protests in the heavily Democratic city. Photographer: Daniel Acker/Bloomberg via Getty Images