There was a brief, strange moment in 2015 when Russell Brand mattered in mainstream British politics. With an election looming, the opposition Labour Party was trailing in the polls against a coalition government that was the very definition of establishment—led by an Eton- and Oxford-educated prime minister in David Cameron and his Westminster- and Cambridge-educated deputy, Nick Clegg, now president of global affairs at Meta. So the Labour leader, Ed Miliband, went seeking the endorsement of Brand, the actor, comedian, and emerging online provocateur whose anti-corporatist screeds to his 9.5 million Twitter followers and 100,000 YouTube subscribers gave him the appearance of a power player. Miliband got Brand’s endorsement but lost the election.Since then, Brand’s reach has exploded. Hi...