The Justice Department has opened "multiple criminal leak investigations" related to the handling of the Trump-Russia investigation, Attorney General William Barr said on Wednesday.

Republicans have long contended that improper and politicized leaks of information from the DOJ and the FBI to media outlets were a serious problem that harmed the credibility of their investigations, and Barr is now looking into it.

During a Senate Judiciary Committee hearing on special counsel Robert Mueller's report, Sen. Chuck Grassley, R-Iowa, told Barr that “there have been a number of leaks coming out of the Justice department and FBI during high-profile investigations.” Grassley pointed out that the 2018 report from DOJ Inspector General Michael Horowitz found “ a culture of unauthorized media contacts … during the Department's investigation of Hillary Clinton for mishandling highly classified information.” And according to Grassley, “during the Russian investigation, the leaks continued.”

Grassley said “leaks undermine the ability of investigators to investigate” and that “leaks to the papers while Congress's questions to the Department go unanswered is unacceptable.” He pressed Barr on the issue, asking him, “What are you doing to investigate unauthorized media contacts by the Department and FBI officials during the Russian investigation?”

Barr assured him that he was already handling it, saying, “We have multiple criminal leak investigations underway.”

[ Related: 5 takeaways from the Barr hearing]

Later in the hearing, Sen. John Kennedy, R-La., quipped, “When you're investigating leaks at the Department of Justice and the FBI, I hope you will include the Mueller team as well.” That was the end of Kennedy's line of questioning, and Barr did not get a chance to reply.

Republicans in Congress have focused on this issue for years now, but they’ve increased their scrutiny as the Mueller investigation reached its end. Back in April, Rep. Devin Nunes, R-Calif., said that he had sent a notice about multiple criminal referrals over to the Department of Justice, including referrals related to leaks.

“There are five direct referrals based on lying, obstruction, congressional investigation, and leaking. We have a global leaks referral, which involves just a few reporters but could involve multiple people. I don't think it's that many people because I think they probably only have a few sources within these agencies,” Nunes said at the time. “And then you have conspiracy referrals. One is based on the manipulation of intelligence. The second one is based on FISA abuse and other matters. So, that's where we stand."

It’s not just congressional Republicans who have warned about criminal leaks. As noted by Grassley, Horowitz, who has a separate FISA abuse investigation underway, thought leaks at the Justice Department were a serious problem, writing in 2018 that “we have profound concerns about the volume and extent of unauthorized media contacts by FBI personnel that we have uncovered during our review.”

Horowitz added: “The harm caused by leaks, fear of potential leaks, and a culture of unauthorized media contacts ... influenced FBI officials who were advising Comey on consequential investigative decisions in October 2016.”

Although “the FBI updated its media policy in November 2017”, Horowitz said his office “does not believe the problem is with the FBI’s policy, which we found to be clear and unambiguous.”

“Rather, we concluded that these leaks highlight the need to change what appears to be a cultural attitude among many in the organization,” Horowitz said.