Sen. Lindsey Graham, R-S.C., vowed Sunday to investigate alleged discussions at the Department of Justice about invoking the 25th Amendment as a way to oust President Trump from office and threatened to subpoena former FBI Deputy Director Andrew McCabe if he refused to testify on the matter before the Senate.

"We're going to find out what happened here and the only way I know to find out is to call the people in under oath and find out, through questioning, who's telling the truth because the underlying accusation is beyond stunning," Graham, the chairman of the Senate Judiciary Committee, said on CBS News’ "Face the Nation."

Graham added that he also plans to subpoena both McCabe and Deputy Attorney General Rod Rosenstein if they won’t voluntarily agree to testify before the committee.

"There is no organization beyond scrutiny," Graham said. "There is no organization that can't withstand scrutiny. And the FBI will come out stronger."

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He said: "But we've got to get to the bottom of it. What are people to think after they watch "60 Minutes" when they hear this accusation by the acting deputy — acting FBI director that the deputy attorney general encouraged him to try to find ways to count votes to replace the president? That can't go unaddressed."

Graham’s comments come on the heels of a Fox News story that reported that former FBI lawyer James Baker, in closed-door testimony to Congress, detailed alleged discussions among senior officials at the Justice Department about invoking the 25th Amendment.

The testimony was delivered last fall to the House Oversight and Judiciary Committees. Fox News has confirmed portions of the transcript. It provides additional insight into discussions that have returned to the spotlight in Washington as fired FBI Deputy Director Andrew McCabe revisits the matter during interviews promoting his forthcoming book.

Baker did not identify the two Cabinet officials. But in his testimony, the lawyer said McCabe and FBI lawyer Lisa Page came to him to relay their conversations with Rosenstein, including discussions of the 25th Amendment.

“I was being told by some combination of Andy McCabe and Lisa Page, that, in a conversation with the deputy attorney general, he had stated that he -- this was what was related to me -- that he had at least two members of the president’s Cabinet who were ready to support, I guess you would call it, an action under the 25th Amendment,” Baker told the committees.

Graham's comments on Sunday come after he floated the idea of a subpoena last week in a comment to Fox News about the Justice Department discussions.

"I would like to know what happened," Graham told Fox News. "You're having a conversation about whether or not you're going to invoke the 25th Amendment. I imagine if the shoe were on the other foot, my Democratic colleagues would want to know about that conversation if it involved a Democrat."

CBS News reported on McCabe’s comments after he told “60 Minutes” that Justice Department officials discussed the possibility of removing Trump via the 25th Amendment and that Deputy Attorney General Rosenstein had offered to wear a wire around the president.

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The 25th Amendment provides a mechanism for removing a sitting president from office. One way that could happen is if a majority of the president’s Cabinet says the president is incapable of discharging his duties.

Since giving the interview to “60 Minutes,” McCabe has since made an about-face, with a spokesperson for the former FBI chief releasing a statement that says McCabe did not "participate in any extended discussions about the use of the 25th Amendment, nor is he aware of any such discussions."

The Justice Department issued a statement calling McCabe’s comments “inaccurate and factually incorrect."

Reports of the discussions of invoking the 25th Amendment and of Rosenstein wearing a wire were reported in The New York Times.