They parted on good terms, agreeing to talk more. Soon enough, it all came undone. That summer, Trump would tell reporters that there were very fine people “on both sides” of the clash between white supremacists and protesters in Charlottesville, Virginia, that turned deadly.

Around that time, Cummings was growing steadily disillusioned with the president. He didn’t believe that what he had told Trump earlier in the year had made any real impression. Phone calls between the two stopped. What had looked like a fledgling alliance between two men of different parties, backgrounds, and races—a rarity in this political era—collapsed. “Now that I watch his actions, I don’t think it made any difference,” Cummings told me after the president’s first year in office. “I thought it had an impact at the moment, but his actions have not shown that.”

This weekend, things took another ugly turn. Beginning yesterday and continuing today, Trump sent a series of tweets blaming Cummings for poverty in his district. Calling Maryland’s Seventh a “disgusting, rat and rodent infested mess,” Trump wrote that “no human being would want to live there.” (Neither the White House nor Cummings’s office responded to my request for comment about the president’s tweets.)

Adam Serwer: The press has adopted Trump’s reality-show standards

One does not have to be much of a sleuth to figure out what’s behind these latest effusions. Minutes before the president sent the tweets, Fox & Friends had aired a report showing trash-strewn streets and decaying buildings in the West Baltimore neighborhood that is part of Cummings’s district. But the real spark may have come Thursday, when the House Oversight Committee, chaired by Cummings, voted to subpoena emails and text messages flowing from White House officials on personal accounts outside government systems, a move that could prove embarrassing to the president’s daughter, Ivanka Trump, and her husband, Jared Kushner. Both have said through their attorney that they used personal accounts while working in the White House, The New York Times reported.

In his tweets, Trump wrote that Cummings “spends all of his time trying to hurt innocent people through ‘Oversight.’” He complained about money going into Cummings’s district and, without presenting any evidence that anything was amiss, asked how much had been “stolen.”

“Investigate this corrupt mess immediately!” Trump tweeted. Who, exactly, should launch such an investigation and what, precisely, should be investigated, Trump didn’t say. But it hardly matters. The message seemed like a brushback pitch aimed squarely at Cummings, a reminder that Trump, as the head of an executive branch that includes the Justice and Housing Departments, possesses a daunting arsenal of retaliatory powers against many of his opponents.