Sen. Mike Lee said Thursday that Rod Rosenstein made a “stunning” admission when the former deputy attorney general told senators he was “not sure” that he read the entire Foreign Intelligence Surveillance Act (FISA) renewal application against former Trump campaign aide Carter Page.

“That was stunning, the fact that he didn’t read the whole application. The fact that he’s willing to sign off on it, not knowing what else might be in there, ” said Lee, a member of the Senate Judiciary Committee, on “America’s Newsroom."

Lee was referring to Rosenstein’s statements during his testimony before the Senate Judiciary Committee on Wednesday. The former Justice Department official who essentially created and oversaw special counsel Robert Mueller’s investigation offered implicit support for a subsequent review of the origins of that case at the FBI and beyond.

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Rosenstein also discussed several issues surrounding the origins of the Russia investigation—including the way in which FISA warrants were sought and approved. He added that he would not have signed a FISA warrant renewal application for Page had he known about the since-revealed misconduct surrounding those warrants -- while faulting the FBI for its handling of the documents.

On Wednesday Rosenstein said, “There are a lot of FISA applications that come through, some are more significant than others. This one was unusual in that I already knew about it because of the Russia investigation.”

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He added that he got it “in advance so I could review it, I’m not sure I read every page, but I was familiar with what was in it.”

“Ultimately the fact that what was in there was incomplete really indicates that we got a serious breakdown with the Foreign Intelligence Surveillance Act, which is why I walked away yesterday with a more profound commitment to make sure that we reform this law,” Lee said reacting to Rosenstein’s testimony.

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“This is bad. This is going to happen to other people. I guarantee it,” he continued. “It’s happened to others that we don’t know about, but we got to fix this thing.”

The Senate passed last month an amendment to the FISA law, proposed by Lee and Sen. Patrick Leahy, D-Vt., that requires FISA court judges to appoint a neutral third-party observer to oversee the process.

Fox News’ Brooke Singman contributed to this report.