Mr. Trump said he would spin the reporters himself. Though his campaign had dispatched advisers and spokeswomen, close congressional allies and even his running mate to the debate “spin room,” where journalists mix with such surrogates, former President Donald J. Trump bucked tradition. He walked into the room full of reporters less than an hour after the end of his debate against Vice President Kamala Harris on Tuesday night and insisted that he’d delivered a winning performance. “It was...