The political mind-set that turned human beings into categories, classes and races also turned them into rodents, insects and garbage. “Anti-Semitism is exactly the same as delousing,” Heinrich Himmler would claim in 1943. “Getting rid of lice is not a matter of ideology. It is a matter of cleanliness.” Watching Warsaw’s Jewish ghetto burn that year, a Polish anti-Semite was overheard saying: “The bedbugs are on fire. The Germans are doing a great job.”

Today, the rhetoric of infestation is back. In the U.S., Trump uses it to describe Latin American migrants. In Europe, Jaroslaw Kaczynski, chairman of Poland’s ruling Law and Justice Party, warned in 2015 that migrants carried “all sorts of parasites and protozoa,” which, “while not dangerous in the organisms of these people, could be dangerous here.”

More of this talk will surely follow, and not just from the right. The American left has become especially promiscuous when it comes to speaking pejoratively about entire categories of disfavored people.