Chairman of the Senate Homeland Security and Governmental Affairs committee Ron Johnson (R-WI) said on Monday that he is moving to subpoena a former Ukrainian diplomat and an American consulting firm tied to Hunter Biden’s service on the board of a Ukrainian gas company. Johnson wrote in a letter to his colleagues on Monday that he is planning to subpoena information from Blue Star Strategies, LLC, a firm that worked with Burisma, as well as Andrii Telizhenko, a former diplomat and consultant for Blue Star. “As part of the Committee’s ongoing investigation, it has received U.S. government records indicating that Blue Star sought to leverage Hunter Biden’s role as a board member of Burisma to gain access to, and potentially influence matters at, the State Department,” Johnson stated.

The letter comes less than two days after former Vice President Joe Biden had a decisive win in the South Carolina Democratic primary. Hunter Biden’s service on the board of Burisma has been under fierce scrutiny by President Trump and his allies, who have asserted that his involvement with the company while his father led the Obama administration’s Ukraine policy was corrupt.