Details: Mr. Firtash, an energy tycoon who is facing extradition to the U.S. on bribery and racketeering charges, said that one of Mr. Giuliani’s associates had offered to intervene on his behalf with the Justice Department.

Response: Mr. Giuliani told The Times that there was nothing improper about his dealings with the oligarchs. “Where do you think you get information about crime?” he said.

Related: After the president’s July call, Mick Mulvaney, the acting White House chief of staff, asked budget officials whether there was a legal justification for withholding $391 million in military aid to Ukraine.

Another angle: Devin Nunes, the top Republican on the House Intelligence Committee, said reports that he had helped efforts to smear Mr. Biden were “demonstrably false.”