When former President Donald J. Trump walked onto the stage at his rally in Atlanta on Saturday, fog machines shot white plumes of smoke into the air, heralding his arrival.

If you looked closely, you could almost imagine steam pouring out of his ears, too. All week long, something had been giving him the vapors.

“Crazy Kamala,” he fumed a minute into his speech. “She was here a week ago — lots of empty seats — but the crowd she got was because she had entertainers.”

Four days earlier, Vice President Kamala Harris had packed about the same number of people (10,000) into the arena, the Georgia State University Convocation Center. It was the first major rally of her newborn campaign, and she had two rappers (Quavo and Megan Thee Stallion) on hand to hype up her crowd.

Mr. Trump, who has been shunned by much of the entertainment industry, spun this as somehow cheating in the all-important competition over crowd size.

“I don't need entertainers,” he said on Saturday. “I fill the stadium because I’m making America great again.”