Two powerful Senate committees are probing alleged Russian meddling in the 2016 election - and possible collusion with the Trump campaign, but only one panel has managed to line up key witnesses.

Both the Senate’s Judiciary and Intelligence Committees are leading separate investigations, but the two panels are dueling for information—and the Senate Intel Committee is winning.

Fox News has confirmed that former FBI director James Comey will testify before the Senate intelligence committee on June 8.

On May 19, the fired FBI chief declined Judiciary’s request to testify—but this wasn’t Judiciary’s first disappointment.

“The Judiciary Committee has primary responsibility for FBI oversight,” Sen. Lindsey Graham, R-S.C., who sits on the Judiciary Committee said when Comey declined the panel’s request. “If former Director Comey testifies, he should do so before both the Intelligence and Judiciary Committees.”

Days after Comey’s May 9 ouster, the Intelligence Committee heard testimony from Acting FBI Director Andrew McCabe. On that same day, Intel committee members met with Deputy Attorney General Rod Rosenstein, who penned a letter to the president recommending Comey’s firing.

The day after, the Judiciary Committee followed Intel’s lead, and requested the same committee briefing with Rosenstein on May 12, and invited McCabe for one as well, but the committee received no response. Judiciary also requested the Comey memos which reflected conversations he had with President Trump regarding the investigation, and former National Security Adviser Michael Flynn, who reportedly will hand over subpoenaed personal and business records to the Intelligence Committee.

“The FBI said it is still reviewing the request to provide Comey memos following the announcement of special counsel,” a Judiciary committee spokesperson told Fox News in an email on Wednesday. “We’ve not heard back on our requests for briefings from McCabe and/or Rosenstein.”

But the Department of Justice downplayed the Judiciary Committee’s concern with a lack of response from Rosenstein, noting he briefed the full Senate May 18.

“This request came in before the Deputy Attorney General appointed Robert Mueller as special counsel and before he had briefed all 100 members of the U.S. Senate,” DOJ Director of Public Affairs Sarah Flores told Fox News. “Since that appointment, briefings related to that ongoing investigation from the Department would now be coordinated with Special Counsel Mueller’s office.”

When asked about a possible McCabe appearance or response to the Judiciary Committee’s request, an FBI spokesperson told Fox News that the bureau works with “all of our oversight committees on their requests.”

But former FBI special agent and former bureau national spokesman John Iannarelli told Fox News that it makes “perfect sense” for top witnesses to choose to provide testimony before Intelligence, rather than Judiciary.

“Choosing the Intelligence Committee over Judiciary makes perfect sense because this is for intelligence purposes—has the president or his staff compromised intelligence?” Iannarelli said. “This is an intelligence-based inquiry, anyway.”

Iannarelli added: “This could also be further indication that nothing is here that actually compromised sensitive intelligence, especially because Comey agreed to testify in an open setting.”

But the Judiciary Committee isn’t giving up. On May 20, Chairman Chuck Grassley, R-IA, took to Twitter and said the Committee would continue.

“JudiciaryCom must continue FBI oversight even w SpecCounsel Can’t wait months for Mueller report Judiciary needs to know so we can act&clear,” Grassley tweeted.

Judiciary Committee Ranking Member Dianne Feinstein, D-Calif., sits on both committees, and will have her opportunity to press Comey when he testifies before the Senate Intelligence Committee.

Feinstein’s office told Fox News they would not comment.

Despite media reports that Comey has been cleared by Special Counsel Mueller to testify in public next week, a Mueller spokesperson told Fox News that he had no information on Comey’s potential testimony, or whether Mueller cleared him for public testimony.

Congress is currently out of session, and will resume business next Tuesday. Comey will testify before the Intelligence Committee on Thursday, June 8, in an open session, followed by a closed session.