Chicken tenders and cynicism were flying through the air. It was Saturday night in Tuscaloosa, Ala., and former President Donald J. Trump was in the bowels of Bryant-Denny Stadium at the University of Alabama, surrounded by screaming football fans. He began hurling boxes of chicken at them. His aides filmed his every movement, uploading the footage to social media. One popular pro-Trump influencer reposted a video of Mr. Trump traipsing through the concourse, writing: “There have been two...