Generalizing about the world at large on the basis of personal success, or proclaiming that life has never been so wonderful, can be politically disastrous, it turns out, especially when loss, decay and fear sum up the experiences of many other people. We will have learned nothing from Mr. Trump’s victory if we do not examine today how and why American elites came to indulge in ressentiment-generating boosterism just as economic and cultural inequality was becoming intolerable to so many, and how their loss of intellectual credibility and moral authority brought about the post-truth era.

The elites’ jauntiness in an age of decline, so weird in retrospect, deviated sharply from the mood of cultural anxiety among American intellectuals during the 1950s, the high noon of American power. With much of Europe and Asia in ruins after World War II, an isolationist country had become world leader. But the very real possibility of another calamitous conflict, this time with a nuclear-armed ideological rival, weighed on the minds and sensibilities of many thoughtful men and women. The recent descent into barbarism of Germany, one of the world’s great industrial, cultural and intellectual powers, had already suggested that much was wrong with modern civilization.

Critics as various as Erich Fromm, Herbert Marcuse, Hannah Arendt, Dwight MacDonald and Richard Hofstadter grappled with the possibility that the individual — disoriented by radical change, detached from traditional faith and other ethical constraints — was prone to manipulation by the machineries of propaganda and entertainment. The titles of some of the decade’s bestsellers — “The Hidden Persuaders,” “The Power Elite,” “The Lonely Crowd,” “The Organization Man,” “One-Dimensional Man,” “Irrational Man” — underlined the new threats that a hyper-rationalist society devoted to profit and consumption posed to human freedom. “Our gadget-filled paradise suspended in a hell of international insecurity certainly does not offer us even the happiness of which the former century dreamed,” wrote Reinhold Niebuhr, whom Mr. Obama has described as an early inspiration.

The unrivaled greatness of America, though a cause for self-congratulation to many, also incited much uneasiness. In a 1960 five-part series in Life magazine about the “national purpose,” which asked if America was “great in the right way,” Adlai Stevenson — a presidential candidate no less cerebral than Mr. Obama — worried that, “self-deceit has slackened our grip on reality.” Arthur Miller, Saul Bellow and Norman Mailer illuminated in their works the contradiction that, as James Baldwin put it, Americans were “afflicted by the world’s highest standard of living and what is probably the world’s most bewilderingly empty way of life.”

The sociologist C. Wright Mills described how an elite connected by Ivy League education and overlapping interests could steal the choicest fruits of American progress. Walter Lippmann worried that the promise of private wealth-creation was a weak moral basis for a national community. For many midcentury thinkers, nihilism, a catastrophic breakdown of faith in national ideology and institutions that had occurred in Europe, was also a possibility in America.