Sen. Lindsey Graham (R-S.C.) requested records from the State Department on Thursday related to then-Vice President Joe Biden’s efforts to oust a Ukrainian prosecutor in 2016.

The letter to Secretary of State Mike Pompeo comes as Republicans seek to train scrutiny on Biden’s actions in Ukraine amid impeachment proceedings against President Donald Trump over his own efforts to pressure Ukraine’s government to investigate his would-be rival for the White House.

Graham is seeking records related to phone calls that occurred in February and March 2016 between Biden and Ukraine’s then-president, Petro Poroshenko, regarding U.S. demands that the country fire its top prosecutor. The prosecutor, Viktor Shokin, was unpopular with Western leaders, who viewed him as corrupt, and Biden was representing official U.S. policy and that of allied governments.