Senate Judiciary Committee Chairman Lindsey Graham on Tuesday formally asked Attorney General William Barr to declassify a huge cache of documents that could shed light on the FBI’s use of surveillance warrants during its Russia and Trump investigations – saying it could help “provide a complete picture of what went on.”

In a letter released Tuesday, the South Carolina Republican requested that Barr work with DOJ Inspector General Michael Horowitz to declassify documents, saying Horowitz’s probe of these warrants is nearing completion.

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“In order for the Inspector General to be able to present the most complete results of his investigation to Congress and the American people, certain documents will need to be declassified and released to the public,” Graham said in the letter, dated Thursday.

Horowitz has probed how the dossier compiled by former British spy Christopher Steele was used to secure the original surveillance warrant for former Trump aide Carter Page in October 2016, as well as for three renewals. Horowitz’s team has questioned why the FBI considered Steele a credible source, and why the bureau seemed to use news reports to bolster Steele’s credibility.

President Donald Trump earlier this year gave Barr the authority to declassify documents related to his campaign surveillance.

In his letter, Graham detailed a wide range of documents he'd like to see, related to nine areas. Among them are documents shared with congressional leaders in 2018 about the Russia probe; the Foreign Intelligence Surveillance Act warrants for Page or anyone else associated with the Trump campaign; a chart that shows the FBI’s attempts to verify the allegations in the Steele dossier; and documents related to so-called defensive briefings given to the Trump and Clinton presidential campaigns in 2016.

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“I write to urge you to declassify all documents the Inspector General identifies as appropriate for declassification as much as possible, without harming national security,” Graham said.

A Justice Department spokesman declined to comment Tuesday.

Horowitz’s office has said the probe is examining “the Department’s and the FBI’s compliance with legal requirements, and with applicable DOJ and FBI policies and procedures, in applications filed with the U.S. Foreign Intelligence Surveillance Court (FISC) relating to a certain U.S. person.”

Graham's letter comes days after Horowitz’s team released its report reprimanding former FBI director James Comey for drafting, leaking and retaining memos of his conversations with Trump. Last week, Graham suggested that the report is just the start of a series of looming rebukes for key law enforcement figures.

“This is the first of what I expect will be several more ugly and damning rebukes of senior DOJ and FBI officials regarding their actions and biases toward the Trump campaign of 2016,” Graham said.