Donald Trump’s outraged response to Manhattan District Attorney Alvin Bragg’s indictment of him contained the usual mix of bombast and self-pity, with a predictable dollop of conspiracy-mongering. One line of attack stood out in particular: He accused Bragg of being “hand-picked and funded by George Soros.” Trump wasn’t alone. The alleged Bragg-Soros connection has been everywhere in the Republican response to the indictment, including in comments from Florida Gov. Ron DeSantis, Ohio Sen. J.D. Vance, and a host of other prominent Republicans and Fox News coverage. It often gets shorthanded into a two-word phrase: “Soros-backed.” Soros, a nonagenarian Holocaust survivor...