“How the hell is Bruce Ohr still employed at the Justice Department?” Trump wrote on Thursday. “Disgraceful! Witch Hunt!”

Trump’s fixation with seeing Ohr ousted from the Justice Department could be perceived as yet another attempt to undermine the credibility of the people who have investigated him. It could also be interpreted as an attack on someone with deep knowledge of the shady characters Trump and his cohort have been linked to, including Semion Mogilevich, the Russian mob boss, and Oleg Deripaska, a Russian aluminum magnate close to Putin who did business with Trump’s former campaign chairman Paul Manafort. (Incidentally, another Manafort associate, the Ukrainian billionaire Dmitry Firtash, admitted that he only managed to be in business because Mogilevich allowed him to be, according to a leaked 2008 State Department cable.) Ohr was involved in banning Deripaska from the U.S. in 2006, due to his alleged ties to organized crime and fear that he would try to launder money into American real estate. Nearly a decade later, Ohr and the FBI sought Deripaska’s help in taking down overseas criminal syndicates.

And then there’s Andy McCabe, the former deputy director of the FBI who spent more than a decade investigating Russian organized crime and served as a supervisory special agent of a task force that scrutinized Eurasian crime syndicates. McCabe is a 21-year FBI veteran who handled aspects of the Russia investigation until Mueller was appointed last May, an appointment McCabe says he pushed for. He was fired in March, just two days short of being eligible to receive his pension and other benefits from the bureau. The official reason was that he had lacked candor when describing his interactions with the press to the Office of the Inspector General. But Trump and his allies’ relentless attacks on McCabe on Twitter and cable news made it difficult for many to believe that Attorney General Jeff Sessions’s decision to fire him was completely devoid of political considerations.

One member of Mueller’s team, meanwhile, has provoked more ire from the president’s allies than others: Andrew Weissmann, a seasoned prosecutor who oversaw cases against high-ranking organized criminals on Wall Street in the early 1990s and, later, against 30 people implicated in the Enron fraud scandal. Trump has also villainized the former Mueller team member Lisa Page, a trial attorney in the Justice Department’s organized-crime section whose cases centered on international organized crime and money laundering. She has been targeted by the president and his allies for mocking Trump in text messages she exchanged with Peter Strzok, a Russian counterintelligence expert in the FBI, during a period in which both briefly worked on the Mueller investigation. Strzok was fired earlier this month for writing similarly caustic messages. Trump says the texts showed outrageous bias and has cited them as evidence that Mueller is out to get him.