The West is abuzz with reports of a populist wave: rolling through Europe, sweeping across the Atlantic, and crashing into Gomorrah-by-the-Potomac. Donald Trump’s election as president of the United States—a watershed event as unthinkable as it was improbable to many across the ideological spectrum of American punditry—followed hard on the British people’s vote to exit the European Union, a cognate popular rejection of bipartisan elite opinion.

In short order, Matteo Renzi was the next shoe to drop. Italy’s now-former prime minister, a young, attractive, politically “progressive” technocrat, darling of the European cognoscenti, had been hailed—it seemed like only yesterday—as Rome’s (or is it Brussels’s?) answer to Barack Obama. He resigned in November, though, after the Italian people resoundingly defeated his proposed const ...