“The American political scene,” wrote Perry Anderson in 2013, “is conventionally depicted in high colour.” According to conventional—that is, liberal—observers in the Bush and Obama years, America “cartwheeled from brutish reaction under one ruler, presiding over disaster at home and abroad, to the most inspiring hope of progress since the New Deal.” Within the broad band of liberal opinion, some mourned the growing divide between thoughtful Democrats and extremist Republicans, while others cheered the rise of “marginalized identities” and the emergence of a new multiracial majority: “the tints change by the light in which they are seen.”

A decade…