Former Deputy Attorney General Rod Rosenstein will be the first witness to testify in the Senate Judiciary Committee’s investigation into the origins of the Russia probe on Wednesday.

Rosenstein will testify about “new revelations contained in the Horowitz report concerning the FISA warrant applications and other matters,” according to Sen. Lindsey Graham, R-S.C, who chairs the Judiciary Committee. "This will be the first in a series of oversight hearings regarding all things Crossfire Hurricane and the Mueller investigation.”

Here’s what to know:

Rosenstein approved the third FISA Renewal Application for Carter Page

On June 29, 2017, both Rosenstein and then-acting FBI Director Andrew McCabe approved the third and final FISA renewal application to surveil former Trump campaign adviser Carter Page. But in January 2020, it was revealed in a DOJ assessment that the surveillance warrants lacked probable cause when stripped of FBI misinformation in the Steele dossier.

However, Rosenstein said he didn’t recall knowing about the political nature of the Steele dossier when signing the Carter Page FISA renewal application.

Rosenstein gave Mueller his full authority to investigate the Russia probe

Rosenstein, in May 2017, appointed Robert Mueller as special counsel.

Rosenstein also penned the “scope memo” for Mueller’s investigation in August 2017, which outlined the authority of Mueller. Earlier this month, the memo was released in full and revealed for the first time that Mueller’s authority went significantly beyond what was previously known.

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The newly released version of the document makes clear that Rosenstein didn't hesitate to explicitly authorize a deep-dive criminal probe into the Trump team that extended well beyond Russian interference efforts.

Additionally, the scope memo stated that Mueller was charged specifically with investigating whether several former Trump officials -- including Page, George Papadopoulos and Paul Manafort -- had "committed a crime or crimes by colluding with Russian government officials with respect to the Russian government's efforts to interfere with the 2016 election for President of the United States."

Rosenstein supported AG Barr's conclusion that the president didn't obstruct justice in the Mueller probe

ROSENSTEIN TO TESTIFY AS FIRST WITNESS IN SENATE JUDICIARY'S PROBE

After Mueller didn't reach a conclusion on whether Trump had obstructed the investigation, Barr and Rosenstein stepped in and determined the evidence wasn't enough to support such an allegation.

In his final months in office, Rosenstein became a frequent target of Trump's ire, after FBI Deputy Director Andrew McCabe described private discussions about secretly recording and potentially ousting the president in the days after he fired FBI Director James Comey. Rosenstein denied pursuing a recording of the president.

Rosenstein was part of a small group of department officials who reviewed the Mueller report originally and helped shape its public release.

Rosenstein's testimony will shape potential subpoenas of top Obama officials

The Judiciary Committee is expected to vote one day after Rosenstein’s testimony on whether to subpoena documents and testimony from top Obama officials.

The potential subpoenas would cover documents, communications and witness testimony in a public setting or behind closed doors for any “current or former executive branch official or employee involved in the 'Crossfire Hurricane' investigation.”

Graham is seeking testimony from former FBI Director James Comey, former FBI Deputy Director Andrew McCabe, former Director of National Intelligence James Clapper, former CIA Director John Brennan, former Deputy Attorney General Sally Yates and others.

The subpoena authorizations would cover any documents, communications and testimony “related to any aforementioned matter” from current and former officials, including Trisha Anderson, James Baker, Dana Boenta, Mary McCord, Andrew McCabe, Loretta Lynch, Jonathan Moffa, Bruce Ohr, Lisa Page, Peter Strzok, Joseph Pientka, John Podesta, Samantha Power, Susan Rice, Bill Priestap, Sally Yates and Rosenstein among others.

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The authorizations would also cover individuals involved in the Steele Dossier, including Fusion GPS founder Glenn Simpson and Nellie Ohr.

Fox News' Brooke Singman contributed to this report.