The problem with socialist governments, Margaret Thatcher famously inveighed in 1976, is that “they always run out of other people’s money.” The problem now confronting many of the world’s political insurgencies is surprisingly similar. Only this time it isn’t precisely the other guy’s money they’re after. It’s the other guy’s control.

The central insight most political analysts claim to offer about electoral upsets—and a central tenet of the self-understanding of the insurgents themselves—is that voters are reclaiming national...