Kevin Johnson, and Erin Kelly

USA TODAY

WASHINGTON — As multiple congressional committees widen their Russia investigations, former FBI director Robert Mueller is emerging as the gatekeeper.

In the past week, since Mueller was appointed to oversee the FBI's ongoing probe into possible collusion between President Trump's campaign and the Russian government, congressional leaders who are also investigating Russia's interference in the 2016 presidential elections have started acknowledging the new special counsel will decide their access to critical witnesses and documents.

Senate and House committee leaders already are engaged in a delicate dance with Mueller to secure documents and public testimony from James Comey, the former FBI director abruptly fired two weeks ago in the midst of managing the Russia inquiry.

Earlier this week, Rep. Jason Chaffetz, R-Utah, chairman of the House Oversight and Government Reform Committee, was forced to cancel a hearing where he sought Comey’s public testimony, saying that the former director needed to consult with Mueller first before offering any public comment.

On Thursday, assistant FBI Director Gregory Brower said Chaffetz's request for a file of documents Comey kept of his communications with Trump would have to wait. "In light of this development and other considerations," Brower said in a letter to Chaffetz, citing Mueller's appointment, "we are undertaking appropriate consultation to ensure all relevant interests implicated by your request are properly evaluated."

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Comey, who maintained kept detailed records of his communications with Trump, has agreed to testify before the Senate Intelligence Committee following the Memorial Day holiday, but committee leaders said they are expected to “coordinate’’ the former director's anticipated public appearance with Mueller. The FBI is still reviewing the Intelligence panel's request for Comey's memos, too.

What's more, embattled former national security adviser Michael Flynn rejected a Senate subpoena for his communications with Russian officials, which have drawn the scrutiny of both the FBI and Congress. By asserting his Fifth Amendment right against self-incrimination, Flynn appeared to acknowledge he might still be in legal jeopardy with Mueller's investigation, which could end in criminal charges.

With at least four congressional panels now seeking records and witnesses, there's mounting tension between interests of lawmakers who are urging a public airing of Russia's interference campaign — and a prosecutor who has long been wary that any disclosure of potential evidence could damage an ongoing criminal investigation.

“I really view the public portion of our investigation as extremely important,” said California Rep. Adam Schiff, the top Democrat on the House Intelligence Committee, which is leading one of the congressional inquiries.

“If we conduct all of our hearings in closed session, do our work in closed session ... and then we throw open the doors when we’re finished and say, ‘Here’s our report, you should just believe it; take our word for it,' it’s unlikely to be accepted by the country," Schiff continued.

Schiff said that the bulk of Mueller's work, meanwhile, will likely be shrouded in secrecy.

If charges are brought, "(Mueller) won’t be able to say much beyond the four corners of an indictment,'' Schiff said.

Chaffetz, for his part, insisted his committee "has its own, constitutionally based prerogative to conduct investigations."

In a separate letter to acting FBI Director Andrew McCabe, Chaffetz did acknowledge “the committee in no way wants to impede or interfere with the special counsel's ability to conduct his investigation. In fact, the committee's investigation will complement the work of the special counsel.’’

So far, the congressional hearings into Russia's election interference have featured news-making public testimony from current and former officials — including former acting attorney general Sally Yates, who first alerted the White House in January that Flynn had lied to administration officials about his contacts with the Russian ambassador. Yates' testimony, quickly followed by Comey's surprise firing, have helped fuel mounting public pressure for the investigations to continue — even as President Trump himself calls the Russia inquiry a "hoax" and "witch hunt."

Despite the public desire to hear from potential witnesses like Comey, whose memos include details of a February meeting with Trump where the president allegedly pressed the then-director to shut down the bureau's investigation of Flynn, legal analysts said there can be inherent risk in allowing witnesses and documents to go public.

And so far, the White House and Justice Department have been reluctant to provide the congressional committees timely access to some documents, including any records detailing conversations between Trump and Comey.

In addition to delaying the Oversight panel's request, the administration also missed a Senate Judiciary Committee deadline Wednesday to turn over Comey's memos and any audio recordings of the president's interactions with Comey that might be maintained at the White House. Instead, they requesting more time to respond to lawmakers' demands. Trump, in a tweet after Comey's dismissal, raised the prospect that "tapes" may exist — and the White House has refused to confirm or deny whether the president secretly records his conversations.

This hasn't deterred lawmakers from their quest to get more information. Senate Intelligence Committee, meanwhile, announced Thursday that it was accelerating the pace of its work. The panel voted to grant Chairman Richard Burr, R-N.C., and Virginia Sen. Mark Warner, the ranking Democrat, "blanket authority'' to issue subpoenas, rather than seek full committee approval.

Still, legal analysts expect that Mueller will likely be reluctant to give the go-ahead on providing Congress evidence that may go public as their inquiries move forward.

"If I'm Bob Mueller, I'm telling Jim Comey something he already knows: 'You aren't going anywhere until I'm done with you,' " said former assistant FBI director Ron Hosko, who headed the bureau's criminal division.

The primary concern in sending key people to testify publicly, Hosko said is the risk of a witness' testimony changing, if only slightly, with each retelling.

"It only gives a halfway decent attorney a chance to pick a case apart based on inconsistent statements,'' Hosko said. Prosecutors also are averse to providing a preview of their cases beyond what is required in charging documents or pre-trial discovery exchanges with defense lawyers, he added.

Jack Sharman, who served as counsel to the House Banking Committee during independent counsel Kenneth Starr's investigation of President Clinton, said allowing for the release of documents and the public testimony of any potential witness in an ongoing criminal investigation "injects a level of complexity'' that can be difficult for prosecutors to manage.

"Oral testimony can sometimes be negotiated (between prosecutors and lawmakers for use in a congressional hearing),'' Sharman said. "But a document is a document. Once it's out there, there's no getting it back.''

"My gut tells me that if he testifies in public ... it will be limited.''

Former federal prosecutor Jeffrey Cramer put it very simply: "For Mueller, there is nothing good'' that can come from congressional testimony from Comey or other potential witnesses.