Sen. Lindsey Graham wants to declassify a key Russia investigation document related to the FBI interview of one of British ex-spy Christopher Steele’s sources, which the Republican believes casts “grave doubt” on the credibility of Steele’s anti-Trump dossier.

Graham, who is leading an investigation of the Trump-Russia investigators as the chairman of the Senate Judiciary Committee, shed new light on his inquiry during a Fox News podcast with former South Carolina GOP Rep. Trey Gowdy on Tuesday. Graham said his team has seen the memo and wants more information from DOJ Inspector General Michael Horowitz’s December report on the Russia investigation to be made public. The senator also claimed that Steele’s dossier was compromised by Russian disinformation.