The Justice Department has no plans to ask a federal court to release potentially thousands of pages of secret grand jury materials relating to special counsel Robert Mueller's investigations of President Donald Trump and top White House and campaign aides – a move that sets up a possible legal brawl between Congress and the executive branch.

"My intention is not to ask for it at this stage," Attorney General William Barr told a House panel during a hearing this week on the Justice Department's budget request for fiscal 2020. He has since elaborated that he doesn't see a compelling legal reason for doing so.

But the move has incensed Democratic lawmakers since Barr, in a four-page letter last month, summarized the Mueller report's top findings that neither the president nor his associates colluded with Russia during the election and that the special counsel drew no conclusion on whether to accuse Trump of obstruction of justice.

Democrats have called on Barr to ask the U.S. District Court for the District of Columbia, where the grand jury was convened, to release materials such as witness testimony and subpoenas – and, separately, to make public an unredacted version of Mueller's report – to provide a full accounting of the special counsel's investigation.

Barr cannot himself release the grand jury materials, which are kept secret in criminal proceedings to protect witnesses, shield ongoing investigations and safeguard the reputations of potential targets who may not be charged with a crime. However, rules governing the disclosure of such materials – which includes testimony by witnesses and subpoenas issued by the grand jury – allow for certain exceptions, including sharing the materials with other judicial proceedings.

The court in 1974, for example, allowed for grand jury materials in the Watergate investigation to be shared with the House Judiciary Committee, which was considering the impeachment of President Richard Nixon, finding that the committee's investigations and deliberations were no different than other judicial proceedings.

At the time, however, Nixon did not oppose sharing the materials. Barr so far has declined to make a request of the court.

"The grand jury material," Barr told a Senate panel this week, "by law must be retained in the Justice Department absent very specific circumstances, which I don't think exist here."

The attorney general appeared to be referring to Rule 6(e) in the Federal Rules of Criminal Procedure, which are promulgated by the courts and which generally limit disclosing grand jury materials.

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Conservative legal scholars have generally held that the rule sets "a presumption of non-releasability," says Charles Stimson, a senior legal fellow at the Heritage Foundation. It's a view that got a boost last week in an obscure 6-year-old lawsuit in federal court in the District of Columbia. A self-published true-crime author in the case was seeking to unseal grand jury records from 1957. The federal appeals court, however, barred their release, ruling 2-1 that courts lack "inherent authority" to share grand jury proceedings and can only do so under one of the few exceptions laid out in 6(e).

"The law right now is in the District of Columbia that the court can only waive 6(e) for one of the grounds specified specifically in 6(e), there's no sort of inherent power in the court to do that," Barr said, seeming to refer to the court's ruling, which came in McKeever v. Barr. "If someone shows me – and I think makes a persuasive argument – that it's covered, I'm willing to listen to that, but I don't see it."

The ruling roiled legal circles: It split from other circuits in the U.S., where courts have more latitude to release grand jury materials.

"How you feel about 6(e) right now depends almost entirely on the policy outcomes you want from the Mueller-Barr investigation," Stimson says.

The ruling, though, applies directly to the District of Columbia, where the Mueller grand jury was convened. Even so, Barr's decision not to even ask for the grand jury proceedings has surprised and drawn criticism from some legal experts.

"That seems to me to be an extremely narrow position to take," says Bill McDaniel, a partner at Ballard Spahr, who represented figures involved in the Iran-Contra scandal and Ken Starr's inquiry into President Bill Clinton. "I've usually been on the side of not disclosing because it can be damaging to your client," but Barr by contrast has indicated he will be "very parsimonious in deciding what to reveal and what not to reveal."

Nick Akerman, a former Watergate assistant special prosecutor, was more blunt: "Any idea that he can't do this or he's not going to do this is outrageous."

The McKeever ruling, pointing to the Watergate investigation, acknowledged a major carveout in 6(e): Impeachment proceedings are equivalent to "judicial proceedings," one of the limited exceptions developed under federal law.

"An impeachment inquiry is similar to a grand jury proceedings," McDaniel says. "The House in essence returns an indictment."

That decision may well make an impeachment effort on the House Judiciary Committee, tamped down by senior Democratic leaders and all but extinguished by Barr's letter last month, suddenly more likely – even if only to get access to the grand jury documents.

"If you were a responsible congressman and leader in the House and said, 'We can't get this material, there's been this big investigation of whether the president committed crimes,' and if the only way we can learn about it is convene an impeachment inquiry, that's what we have to do," McDaniel says.

The Judiciary Committee's chairman, Rep. Jerrold Nadler, D-N.Y., could submit such a request himself if Barr refuses. The materials – which could include more than 2,800 subpoenas and may number into millions of pages – could prove instrumental. In 1974, Akerman recalls, they played a pivotal role in bringing the House Judiciary Committee up to speed.