This is an old article from the NYT, from 2008-- it’s very interesting to reread it now, with all the hatred of Obama over the past few years:
Consider, for starters, this paradox of social psychology, a problem for myth busters everywhere: repeating a claim, even if only to refute it, increases its apparent truthfulness. In 2003, the psychologist Ian Skurnik and several of his colleagues asked senior citizens to sit through a computer presentation of a series of health warnings that were randomly identified as either true or false — for example, “Aspirin destroys tooth enamel” (true) or “Corn chips contain twice as much fat as potato chips” (false). A few days later, they quizzed the seniors on what they had learned.
The psychologists expected that seniors would mistakenly remember some false statements as true. What was remarkable, though, was which claims they most often got wrong — the ones they had been exposed to multiple times. In other words, the more that researchers had stressed that a given warning was false, the more likely seniors were to eventually come to believe it was true. (College students in the study did not make the same mistakes.)
I’ve often thought this about internet trolls- if you repeat their claims, even if only to refute them! —it just increases people’s willingness to believe the claim, and there’s some kind of weird feedback mechanism where the troll gets joy out of the repetition of their slander.