Senate Judiciary Committee Chairman Lindsey Graham (R-S.C.) sent a letter to Secretary of State Mike Pompeo requesting documentation on former Vice President Joe Biden and his son Hunters work in Ukraine on Thursday, as the weeks public impeachment inquiry hearings in the House drew to a close.

In his two-page letter, Graham asked for a number of call transcripts, notes and communications involving Joe Biden, former Ukrainian President Petro Poroshenko, former Secretary of State John Kerry, a former Ukrainian prosecutor and people connected to the Ukrainian energy company Burisma.

While the impeachment proceedings target President Donald Trump s dealings with current Ukrainian President Volodymyr Zelensky, Trumps Republican supporters have attempted to steer the discussion toward the Bidens , claiming that the father-son pair were involved in Ukrainian corruption.

The anti-Biden theory may stem from the work of right-wing columnist John Solomon, who has used his writing to elevate questionable sources. Although no evidence has emerged to support the theory, some Republicans are now loudly alleging that then-Vice President Biden pushed Ukraine to fire a prosecutor, who may or may not really have been investigating Burisma, in order to shield Hunter Biden, who served on Burismas board at the time.

In fact, many officials back then including Republicans thought that the prosecutor in question was ineffective against corruption and that his office needed to be reformed. That was a view shared by the Obama administration and key European allies.

Nevertheless, Graham made a tenuous connection between Hunter Biden and Ukrainian corruption in his letter. On the same day in 2016 that Ukrainian officials raided the home of Burismas founder, Graham wrote, Hunter Biden began following a State Department official on Twitter. Graham suggested that fact indicated that the two may have initiated conversations regarding Prosecutor General [Viktor] Shokins investigation into Burisma. The date was Feb. 4, 2016.

In the weeks afterward, Graham wrote, Joe Biden held several phone conversations with then-President Poroshenko to discuss removing Shokin over allegations that he himself was corrupt. The prosecutor was removed on March 29, 2016.

Grahams request covers communications between the parties from the day Hunter Biden followed then-Deputy Secretary of State Tony Blinken on Twitter to the day of Shokins ouster.

The senator did not specify a deadline for the materials delivery.

In the ongoing impeachment inquiry, witnesses have bolstered allegations that Trump leveraged military aid and a coveted White House meeting to improperly pressure the current Ukrainian president to investigate the Bidens.

Joe Biden is among the many Democrats seeking to take on Trump in the 2020 presidential election and several national polls have consistently shown Biden leading the president in hypothetical match-ups.

Language has been adjusted to clarify allegations relating to Victor Shokin.