Back when he was just a New York real estate developer, Donald Trump often complained about pernicious “infestations” that would bring down his property values. In a 1992 interview, Trump told Charlie Rose about the area of Manhattan where he hoped to build the Riverside South complex: “We’re looking to get zoning for a piece of land that’s unzoned, that’s employing no people, that’s sitting there rotting. It’s rat-infested.”

Three years later, after Trump became a co-owner of the Empire State Building, he tried to oust the building’s management company, run by his nemeses Leona and Harry Helmsley, by filing a lawsuit in which he claimed that the Empire State had become nothing more than a “tarnished, second-rate, rodent-infested commercial building.”

And in 2010, annoyed at delays in bringing an enormous banquet facility called “Trump on the Ocean” to Jones Beach State Park, Trump griped that the only thing visitors could see was “a rat-infested dump.” (Hurricane Sandy finally scuttled Trump’s beachfront boondoggle two years later.)

As president, Trump is still fixated on infestations, but now he wields that language against those he sees as political foes, especially people of color. He tweeted Saturday that the majority-black Baltimore district of Rep. Elijah Cummings was a “disgusting, rat and rodent-infested mess” where “no human being would want to live.” That followed his notorious tweet of July 14 in which he told four progressive congresswomen of color to “go back” to “the totally broken and crime-infested places from which they came.”  […]