A key Republican member of the House Judiciary Committee says the Obama Justice Department has some explaining to do.

Special counsel Robert Mueller's inability to find collusion between President Trump's campaign and Russia begs the question of why officials sought FISA warrants to wiretap one-time campaign adviser Carter Page, Rep. John Ratcliffe, R-Texas, said Sunday on Fox News.

He said Attorney General William Barr, who recently testified "spying did occur" on Trump's campaign, needs to seek answers.

"I'm glad that he has focused on getting the Mueller report out in a redacted form that people can see, but now his focus needs to be answering his own question, as he said, there was spying, the Obama Justice Department and intelligence community did spy on the Trump campaign," Ratcliffe said on "Sunday Morning Futures."

"The question now that needs to be answered is was there a predicate for that?" he added. "Particularly when the predicate was supposedly that there was collusion. Now we know there's no evidence of collusion. Again Bob Mueller didn't say if there was insufficient evidence of collusion. He said, 'No evidence.' He said, 'There isn't any evidence.' So if there wasn't any evidence of collusion what was the probable cause, what was the predicate for the Obama Justice Department to go to the FISA court and represent that there was probable cause of a crime of a conspiracy with Russia and the folks that made those verifications, they got some explaining to do."

Barr is expected to testify about the Mueller report in the next couple weeks. Barr, who sparked an uproar among Democrats earlier this month when he said "spying did occur" on the Trump campaign, is putting a team together to look into surveillance abuse,

Ratcliffe, a former federal prosecutor, said he hopes both Barr and Mueller can illuminate Congress on why the infamous Trump dossier was left out of the report and explain the "troubling origin" of the FISA warrants taken out on Page.

"Remember that the Obama Justice Department didn't just go to the FISA court and represent there was probable cause of collusion that we now know didn't exist on a single occasion," Ratcliffe said. "They did so four times over a year, and so how is that allowed to happen and what steps is he taking, what investigations are underway, and what assurances can he give the American people that there will be accountability for folks who made false verifications about a dossier that was unverifiable because it was untrue."

The dossier, compiled by ex-British spy Christopher Steele, contained salacious and unverified claims about Trump's ties to Russia. It was used by the FBI obtain a series of Foreign Intelligence Surveillance Act warrants to wiretap Page. The first warrant application was submitted in October 2016, after which there were three renewals at three-month intervals, including in January, April, and June 2017.

Page was investigated over his interactions with Russians but was never charged by Mueller.

Ratcliffe has been an integral GOP investigator questioning top brass in the Justice Department and FBI in an investigation examining possible political bias. Last week, House Intelligence Committee Chairman Devin Nunes, R-Calif., sent a notification letter to Barr saying his team "identified several potential violations of the law" as part of an investigation into origins of the Trump-Russia investigation and hopes to set up a meeting with Ratcliffe and himself to discuss eight criminal referrals.