OH, FOR THE GOOD OLD DAYS....

Nostalgia was originally regarded as a disorder by the 17th-century Swiss physician Johannes Hofer, who coined the term after observing that war veterans' debilitating mental ailments seemed rooted in their yearning to return home -- nostos in Greek, and the associated pain, algos. Classic Hollywood was shrewdly keyed into the insight that nostalgia flares up as a defense mechanism when life goes off the rails -- think of Norman Bates pinning on a wig to resurrect his mother in "Psycho" or Norma Desmond entombed in delusions of her silent-era film success in "Sunset Boulevard."

But it's in the political realm where things get interesting. Here, nostalgia empowers demagogues to conjure an idealized past stripped of complexity and then scapegoat the vulnerable to explain the mess of modernity. Instead of inspiring hope-driven projects of innovation and discovery, nostalgia pushes us toward fantasies of restoration: the Islamic State's project to restore the caliphate, the deglobalizing Brexit debacle, Russia's reawakened ambitions for imperial conquest, and, most obviously, Donald Trump's mantra "Make America Great Again," which led directly to the imperative, in the former president's own words, to root out "the sick, sinister, and evil people from within our own country." Nostalgia, in its backward quest for purity and simplicity, can sharpen antagonisms, gin up fears of invasion, and set off stampedes of retribution.

The power of nostalgia to foment political persecution is visible in the flagrant racism of some of the most iconic American films. The release of D.W. Griffith's "Birth of a Nation" in 1915 swelled a moribund Ku Klux Klan to 6 million members. The movie promulgated a myth of white purity under siege by immigrants, Catholics, and, most of all, Black Americans, and the KKK then carried out terrorist campaigns, including cross burnings and lynchings, to realize that ideal of white supremacy.

Margaret Mitchell's 1936 novel "Gone with the Wind," and the film that appeared three years later, invoked, with dewy sentimentality, the antebellum South as an agrarian, courtly world of cotton, cotillions, and gentility, harmoniously organized in a benevolent caste system. This simple, beautiful world gets crushed before our eyes by Northern aggressors and General Sherman's army of invaders, who strip and burn plantations to the ground to make way for a further invasion by greedy carpetbaggers. To restore the luster of her plantation home, Scarlett O'Hara has to degrade herself by becoming a scrappy business owner and beating the Northerners at their own game. As she sacrifices her nobility and innocence, audiences are led to mourn a lost Eden -- a civilization that is gone with the wind. The film's nostalgia proved chillingly effective at obscuring the brutality of plantation slavery and at fueling scapegoating and resentment in the segregated era of the late 1930s and for decades after.

Movies that romanticize the past also tend to malign the hard-fought struggles that extended political equality. "Forrest Gump" is a revealing example. Here, morality is reducible to the homespun folk wisdom that life is like a box of chocolates, while the narrative stigmatizes forces pushing for political reform. The civil rights movement gets epitomized by a Black Panther member's outburst of domestic battery. Hippies are drug-snorting hedonists nihilistically teetering on the edge of suicide. The sexual revolution produces the scourge of AIDS. The message appears to be that there was a beloved past underpinned by basic decency and familial love, values that were polluted by the decadent era of sex, drugs, and political agitation.

Matthew Leggatt, a senior lecturer in literature at the University of Winchester in the UK, says that part of the allure of nostalgia is that it allows us to revert to childhood, with the freedom of feeling unburdened by moral responsibility -- or by the obligation to build a more decent future. "Cultural nostalgia," he says, "doesn't let us look ahead with an eye toward innovation and utopian aspirations."

"A River Runs Through It" offers evidence that a more honest reckoning is possible.

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