But the vagueness of the concept served only to heighten hysteria. “Menticide,” announced the Columbia University psychiatrist Joost Meerloo, was a crime against humanity analogous to — or even worse than — genocide. The conceit spawned an array of nightmare scenarios. The worst of them appeared to be confirmed when 21 American prisoners refused repatriation after an armistice halted the Korean War in July 1953. Since a preference for “Red China” over America seemed inconceivable to many contemporaries, the conclusion was that the men must have been brainwashed. An unequivocal New York Times editorial in January 1954 evinced no doubt whatsoever. The “non-repatriates” offered “living proof that Communist brainwashing does work on some persons,” The Times informed its readers.

Fixated on these “turncoat G.I.s,” United States commentators tended to forget that an inordinately greater number of North Korean and Chinese P.O.W.s had refused repatriation to their side. What might have registered as a symbolic victory for the “free world” — 22,000 to 21 — was lost in heated contention over how brainwashing was performed and why Americans had seemingly succumbed en masse.

A vast majority of American P.O.W.s who survived captivity did return home — as, eventually, did almost all of the 21 men supposedly lost to brainwashing. But many found themselves suspected as traitors or ideological termites, sent back by their Communist captors to hollow out American society from within. Insidious plots subsequently made popular by fiction — think “The Manchurian Candidate” — appeared first in the pages of serious newsmagazines. In The Saturday Evening Post, Rear Adm. D. V. Gallery speculated that the Communists had expended so much energy on brainwashing American P.O.W.s to create a network of sleeper saboteurs awaiting activation. The Chinese, according to Admiral Gallery, had sown mental seeds they anticipated would “take root” and sprout in 10 or 20 years should another depression grip America. “This may seem far-fetched to those of us who live from year to year,” he acknowledged, before adding an Orientalist twist to his scenario. “But it isn’t to Asiatics, who look at centuries as we do months.”

Why did people take “brainwashing” so seriously, despite the best efforts of prominent social scientists to debunk outré Pavlovian notions and the racist stereotypes often used to buttress them? And why does “election hacking” exert a comparable allure? Anxieties about external manipulation are not, of course, divorced from the demonstrable efforts of other powers to sway Americans’ politically consequential behavior: The theft and distribution of Democratic National Committee emails was real enough, as was the Chinese effort to win converts among captive Americans imprisoned in North Korea. But “election hacking” and “brainwashing” share an aura of dark magic that obscures the precise mechanics believed to be at work in shaping the thoughts and actions of freethinking adults. And obscurity provides fertile soil in which conspiracy theories flourish. When everything is, or may be, a form of “election hacking,” the techniques appear worrisomely diffuse. So, too, do the agents of a phenomenon variously attributed to Russian trolls, Twitter-bots, Facebook ads, a “useful idiot” in the White House or American idiocy more generally.