What gave it away? The slumped shoulders? The slurry speech impediment? The stalling for time each time he is asked a question or any time he is expected to say something intelligent? The flabby gut? The vaginal crease he calls a neck? The fake tan? The combover?
Canceling the CNBC interview I could see after getting thumped in Chicago, but canceling a softball rally where he would certainly be lavished with obsequious adulation suggests a health issue. Undoubtedly the grueling campaign trail is taking its toll on him.
Or a security issue. Very possible that someone called in a threat and Trump pulled out rather than risk a giant crowd full of gun-enthusiasts hiding someone with less enthusiastic views.
After pissing off everyone in a country full of people who have free access to firearms .... I wouldn't want to speak to a room full of these nutjobs myself