"You all know this one," Boston said. With his wife, he raised a banner, one of the first flags of the American Revolution. It bore a coiled snake, a native American viper, with the legend: DON’T TREAD ON ME. A sinister, scaly rattling poured from the depths of a synthesizer, merging with the crowd’s roar of recognition, and a sprung, loping rhythm broke loose. Boston edged back and forth at the stage’s rim, his eyes fixed, his long neck swaying. He shook himself like a man saved from drowning and leaned into the microphone.