President Trump on Tuesday appeared to urge his attorney general to fire Justice Department official Bruce Ohr, who was a contact for the author of a dossier that is the focus of Trump allies trying to discredit the probe into Russia’s interference in the presidential election.

“Where is Jeff Sessions?” Trump wrote in the first of two tweets focusing on Ohr and what is known as the Steele dossier, which detailed allegations about the president’s personal and financial ties to Russia.

“Is it really possible that Bruce Ohr, whose wife Nellie was paid by Simpson and GPS Fusion for work done on the Fake Dossier, and who was used as a Pawn in this whole SCAM (WITCH HUNT), is still working for the Department of Justice?????” he continued in a second tweet. “Can this really be so?????”

Trump’s tweets came only moments after a joint House panel attempted to conduct a closed-door interview with Glenn Simpson, the head of Fusion GPS, a firm behind the dossier compiled by former British intelligence agent Christopher Steele.

Nellie Ohr, a Russian-history expert, worked as a contractor for Fusion GPS during the period when the firm was affiliated with Steele; she is also married to Bruce Ohr, a specialist in countering Russian organized crime who met on several occasions with Steele.

Simpson, who appeared for the closed-door session Tuesday under subpoena, invoked his Fifth Amendment right against self-incrimination. His attorney decried the committees’ proceedings as “an utter sham” that would “make Senator Joseph McCarthy proud.”

“This committee has destroyed the reputations and careers of prosecutors and agents, it has gratuitously exposed personal aspects of their private lives, it has levied false accusations of criminal wrongdoing against them, and this mistreatment is no different as applied to our client,” Simpson attorney Joshua Levy told reporters. “Rather than continue any further in this charade, Mr. Simpson has proudly stood today on his constitutional privileges not to testify.”

One panel member, Rep. Mark Meadows (R-N.C.), questioned whether Simpson had the legal right to refuse to answer Congress’s questions.

“Glenn Simpson has to have a reasonable apprehension of criminal prosecution to validly invoke the Fifth,” he told reporters after the brief interview. “If not, you can’t just invoke the Fifth to avoid answering congressional questions.”

Simpson is one of several witnesses the House Judiciary and Oversight committees plan to interview this month as part of a probe into how FBI and Justice Department officials conducted themselves during investigations of Trump’s Russia ties and former secretary of state Hillary Clinton’s use of a private email server.

The panels plan to speak with former FBI general counsel James Baker on Thursday for the second part of an interview that began last week; they are also expected to interview Nellie Ohr on Friday.

They are also attempting to schedule interviews with Deputy Attorney General Rod J. Rosenstein and former Trump campaign staffer George Papadopoulos for next week.

Simpson’s attorneys are not the first witnesses or participants in the joint probe to complain that the investigation is biased in favor of the president. Democrats have complained, as Levy did Tuesday, that Republicans have forced witnesses to keep silent about their testimony while they leak details to skew coverage of the probe.

“Unfortunately, if you’re not one of the president’s men, these congressional Republicans will show utter disdain for your constitutional rights,” Levy said, complaining that the GOP members of the panels were refusing to focus on “the big picture” of Russian election interference, in favor of nitpicking at the details of the dossier.

“If you want to quibble with one detail here and there, you’re losing the big picture. . . . The Russians tried to elect Donald Trump president — it’s been proven,” Levy said. “The big picture is that a foreign hostile power was trying to interfere in our democracy, in our election.”

Meadows, who was one of only two House members to participate in Tuesday’s closed-door session, shot back at Levy, accusing him of trying to have “an Avenatti moment” in lodging his complaints with the panel publicly. He was referring to Michael Avenatti, the attorney for adult-film actress Stormy Daniels,who alleges that she had an affair with Trump.

“There’s been no evidence of collusion, and that’s where the dossier has its foundations,” Meadows said, stressing that “the Simpson testimony is critically important to getting to the truth.”

“I would expect nothing less than for [Levy] to attack the credibility of this investigation,” Meadows added. He would not say whether the panel expected to hold Simpson in contempt for invoking the Fifth amendment in response to the panel’s questions.

Simpson has appeared before three other congressional panels as part of their investigations, for a total of over 25 hours of testimony, his attorneys said. Rep. Bob Goodlatte (R-Va.), chair of the House Judiciary Committee, insisted Tuesday that their questions were unique.

“We expected Mr. Simpson to answer questions that have not been explored by other congressional committees,” he said in a statement that called Simpson’s refusal to offer detailed answers “disappointing” and complained that he had “denied the American people answers to important questions.”