The chairman of the Senate Judiciary Committee is accusing Deputy Attorney General Rod Rosenstein of providing an “insufficient” response to requests for documents about the investigation of former national security adviser Michael Flynn.

“This is no ordinary criminal case,” Iowa Sen. Chuck Grassley wrote in a letter Wednesday to Rosenstein, who is overseeing the special counsel’s investigation. “It is at the heart of a political firestorm over the President’s alleged statements about it to the former FBI Director, whom he later dismissed. Congress has a right to know the full story and to know it now.”

Grassley, a Republican, has requested documents and interviews to help figure out whether the FBI believed that Flynn lied during a Jan. 24, 2017 interview about his contacts a month earlier with Sergey Kislyak, the Russian ambassador to the U.S. (RELATED: Grassley Flags ‘Apparent Contradictions’ In Comey’s Testimony About Michael Flynn)

Flynn pleaded guilty on Dec. 1 to lying to FBI agents about those contacts. He reportedly denied discussing sanctions with Kislyak, though it has been reported that sanctions were mentioned in their conversation.

Grassley wants to see a transcript of the Flynn-Kislyak interaction as well as notes from Flynn’s first FBI interview.

The Republican noted “public skepticism” towards the Justice Department and FBI because of the fact that details from transcripts of Flynn’s conversation with Kislyak were illegally leaked to the media. Grassley also noted that one of the FBI agents who interviewed Flynn is Peter Strzok, the deputy counterintelligence official who was removed from the special counsel investigation because of his anti-Trump text messages.

Grassley also pointed to “inconsistent” statements from former FBI Director James Comey about Flynn’s case.

In a May 11 letter to Rosenstein, Grassley said that Comey had contradicted himself in media interviews about Flynn. Comey told the Judiciary Committee and the House Intelligence Committee that the FBI agents who interviewed Flynn did not believe that he was lying during the January 2017 interview.

Comey told ABC News and Fox News in interviews for his book tour that he never said he believed that Flynn did not lie to the FBI.

Flynn was forced to resign as Trump’s national security adviser on Feb. 14, 2017. The White House said it was because Flynn lied to Vice President Mike Pence about his conversations with Kislyak.

Grassley said his committee has the right to review records that could get to the bottom of what Flynn said in his FBI interview.

“The Committee has waited patiently for much more than a year for the criminal inquiry related to Lt. General Flynn to conclude,” Grassley wrote to Rosenstein. “It has been more than five months since his guilty plea. Thus, there is no longer any legitimate reason to withhold facts from the Senate about the circumstances of his conversations with the Russian ambassador and his FBI interview.”

Grassley also criticized Rosenstein for refusing to make Joe Pientka, one of the FBI agents believed to have interviewed Flynn, available for an interview with the Judiciary panel.

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