Senate Homeland Security Committee Chairman Ron Johnson, R-Wis., told “Sunday Morning Futures” that Senate Republicans’ investigation into the Russia probe “is going to be centered on” answering the “basic” questions, “Who knew what and when did they know it?”

Johnson made the comments three days after the Senate Judiciary Committee approved subpoenas for documents and testimony from top Obama administration officials as part of the panel’s investigation into the origins of the Russia probe during the 2016 presidential election.

In the exclusive interview Sunday, Johnson said other questions that he wanted answered involved leaks around the time President Trump took office: “Who did all these leaks? What was the purpose of these leaks? Were they trying to cover something up?... Or, was it simply to delegitimize the election and sabotage this administration?”

He noted that “those are the basic questions” Senate Republicans were going to be “asking and hopefully [will] get the answers for the American public because transparency is all about getting the truth out so the American people understood what happened, so hopefully it’ll never happen again, this corruption-of-transition process.”

Johnson then went on to explain what he thought was “very interesting about [former Deputy Attorney General] Rod Rosenstein’s testimony” earlier this month, during which Rosenstein said he would not have signed a surveillance-warrant renewal for former Trump campaign aide Carter Page had he known about misconduct surrounding those warrants.

Johnson went on, “There was an astonishing lack of curiosity and management oversight regarding an investigation into the sitting president of the United States.”

During his testimony before the Senate Judiciary Committee earlier this month, the former Justice Department official, who essentially created and oversaw then-Special Counsel Robert Mueller’s investigation, discussed several issues surrounding the origins of the Russia investigation—including the way in which Foreign Intelligence Surveillance Act [FISA] warrants were sought and approved.

Rosenstein also faulting the FBI for its handling of the FISA documents.

FORMER ACTING DNI GRENELL ON DECLASSIFYING RUSSIA PROBE DOCS: 'TRANSPARENCY IS NEVER POLITICAL'

“I look at Rod Rosenstein and I go, ‘Well either it was willful ignorance, complete managerial incompetence or he simply wasn’t being truthful,’” Johnson said. “I want to get to the bottom of who knew what and when did they know it.”

Host Maria Bartiromo asked Johnson, “Will you be able to get to the bottom of it?”

She pointed out that the “whole time when Rosenstein was testifying he said, ‘I didn’t hear that. I didn’t know that, had I known that I wouldn’t have signed the warrant, I didn’t know that.’”

“I’m sure there’s going to be an awful lot of claims of managerial incompetence because it’s a lot better than really admitting that you did something wrong, something illegal, but we’re going to first start out with a thorough review of the documents,” Johnson responded.

He went on to say, “We’re in a better position than what [former House Intelligence Committee Chairman] Devin Nunes was in the House a couple years ago when they were undertaking those interviews because we know so much more.”

He added, “We’ll have additional documents and now we have a lot more information, so I think our interviews will probably be a lot more interesting, a lot more revealing.”

CLICK HERE TO GET THE FOX NEWS APP

He then noted, “We’re going to have people not recall certain things.”

Fox News’ Brooke Singman and Fox Business’ Maria Bartiromo contributed to this report.