Former President Trump will rally supporters Monday evening at Indiana University of Pennsylvania, about 55 miles east of Pittsburgh. The Keystone State is a crucial prize in November's electoral count, and both campaigns have been working hard to win over voters in the state. The Harris campaign deployed mobile billboards to Indiana, Pa., on Monday chiding Trump for his refusal to accept a second debate. Monday's appearance also brings the former president within 50 miles of Butler, Pa., the site of the July 13 attempt on his life. The Secret Service recently made public the results of an internal review of its response to the shooting, and it acknowledged communication and protocol failures that may have left Trump vulnerable. Trump is slated to appear today at 7 p.m. EDT. Watch the live video above.