WHEN DONALD TRUMP uttered the word “Springfield” 33 minutes into the American presidential debate on September 10th, David Muir, the co-moderator, was prepared. In that small Ohio town, Mr Trump declared, illegal immigrants are “eating the dogs, they’re eating the cats, they’re eating the pets of the people who live there”. Mr Muir promptly replied that, according to Springfield’s city manager, there were no credible reports of pet-eating. The former president’s claim must have struck many viewers as bizarre. But lots of Mr Trump’s fans were primed for it: the allegation had been circulating in right-wing circles on social media, boosted by Elon Musk, the owner of X. How did the town come to be at the centre of a right-wing conspiracy theory?