First he went after the prosecutors who recommended a multiyear sentence for his friend Roger Stone. Then President Trump turned his Twitter ire to the “witch hunt disgrace” of special counsel Robert S. Mueller III’s investigation, which led to Stone’s indictment. But perhaps most surprising was Trump’s decision to target U.S. District Judge Amy Berman Jackson — who will determine Stone’s fate when he appears in her courtroom next Thursday.

When President Trump publicly demanded that the Justice Department open an investigation into the F.B.I.’s scrutiny of his campaign contacts  with Russia, he inched further toward breaching an established  constraint on executive power: The White House does not make decisions about individual law enforcement investigations.