Democrats’ anticipation for public testimony by special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE is building by the minute.

The demands for Mueller to testify before Congress reached a new level of urgency this week, after internal correspondence was revealed to show Mueller objected to Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE’s handling of his investigative findings in late March.

The revelations prompted Democrats to amplify their distrust of Barr over his disclosures about the Mueller report’s remarks on obstruction of justice while whetting the appetite for testimony from the special counsel that now appears likely in the House later this month.

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House Majority Leader Steny Hoyer Steny Hamilton HoyerOVERNIGHT ENERGY: California seeks to sell only electric cars by 2035 | EPA threatens to close New York City office after Trump threats to 'anarchist' cities | House energy package sparks criticism from left and right House energy package sparks criticism from left and right Hoyer: House should vote on COVID-19 aid — with or without a bipartisan deal MORE (D-Md.) stressed that the testimony is vital, given Mueller’s evident frustrations with Barr's summary assessment of the 448-page report.

"I hope that he is desirous of testifying so that he can, from his perspective, talk to the American people, and to the representatives of the American people, on what his views are," Hoyer told reporters this week. "Clearly, this letter indicates that they are not being represented by Attorney General Barr."

"This is a two-year effort, a little short of that, [and a] major investment," Hoyer added. "And I think the American people are justified in hearing his view as to what he found and the interpretation he put on it."

Other Democrats suggested Barr’s testimony cannot be trusted on its own.

"Mueller has to testify," said Rep. Ro Khanna Rohit (Ro) KhannaThe Hill Interview: Jerry Brown on climate disasters, COVID-19 and Biden's 'Rooseveltian moment' Congress needs to prioritize government digital service delivery DeJoy defends Postal Service changes at combative House hearing MORE (D-Calif.). "I think that will be determinative. No one in this country, no one in this body, has more credibility than Bob Mueller. He's the one person who's been circumspect. He's showed humility. I think the American people are going to hear him and make a determination."

Democrats are angling for Mueller to testify on May 15, House Judiciary Committee Chairman Jerrold Nadler Jerrold (Jerry) Lewis NadlerDemocrats shoot down talk of expanding Supreme Court Schumer: 'Nothing is off the table' if GOP moves forward with Ginsburg replacement Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-N.Y.) told reporters this week, though no formal agreement had been reached as of Friday.

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The panel has reportedly been engaging directly with Mueller on a date for his testimony; a committee spokesman did not respond to a request for more information on those negotiations.

Peter Carr, a spokesman for the special counsel, told The Hill in an email Friday that he didn’t have "any information to provide at this time" with respect to negotiations surrounding Mueller’s potential testimony.

Mueller’s appearance in a public setting on Capitol Hill would be nothing short of historic. Lawmakers and voters would have the opportunity to hear from the man who supervised one of the most politically charged investigations while under constant attack from President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE.

Ultimately, Mueller did not establish that members of Trump’s campaign conspired with Russia to interfere in the 2016 election, and he did not reach a conclusion on whether Trump obstructed justice.

Democrats would undoubtedly question Mueller on his interactions with Barr, particularly during the four-week period between the completion of his 22-month investigation and Barr’s public release of the report on April 18. They’re also likely to ask for his candid thoughts on Barr’s March 24 memo to Congress spelling out the report’s bottom-line conclusions.

"At this point, I think we need to hear directly from the special counsel about his report and about his findings," Rep. Pramila Jayapal Pramila JayapalDHS opens probe into allegations at Georgia ICE facility Progressive Caucus co-chair: Whistleblower complaint raises questions about 'entire detention system' Buttigieg, former officials added to Biden's transition team MORE (D-Wash.) told reporters on Thursday. "Clearly, he felt troubled enough by what Attorney General Barr did and said that he wrote not one but two letters to the attorney general."

Mueller’s team reached out to the Justice Department with concerns on March 25, and two days later the special counsel wrote to Barr saying the memo to Congress "did not fully capture the context, nature, and substance” of the investigation's conclusions and created “public confusion” about the results.

Barr testified on Wednesday to the Senate Judiciary Committee that he spoke to Mueller by phone about the March 27 letter. The attorney general later described the correspondence as "snitty" and said it was "probably written by one of [Mueller’s] staff people."

"I asked him if he was suggesting that the March 24 letter was inaccurate, and he said no but that the press reporting had been inaccurate," Barr said.

Mueller’s letter made no mention of press coverage, raising the odds that Democrats are likely to ask the special counsel about Barr’s characterization of that conversation.

Lawmakers would almost certainly press Mueller on why he did not come to a conclusion on whether Trump obstructed justice, something that perplexed many in Washington, including Barr.

Democrats may also look to Mueller to elicit more information about his investigation and report, roughly 10 percent of which was redacted to conceal information related to ongoing probes, grand jury material, national security information and details that impact third parties.

Nadler has subpoenaed for the full report and underlying evidence. The Justice Department has refused to comply, describing the subpoena as "not legitimate oversight" and its requests as "overbroad and extraordinarily burdensome."

Barr has instead allowed select members of Congress, including Nadler, to view a less redacted version in a secure room as long as they agree to keep those contents of the report confidential.

Mueller’s potential testimony appears less likely in the Senate, though Judiciary Committee Chairman Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) on Friday wrote to Mueller to offer him the opportunity to testify before the panel about any misrepresentation by Barr of their phone call.

Graham had otherwise shut the door on hearing from Mueller.

"I'm not going to do any more. Enough already. It's over," Graham told reporters after Barr’s hours-long testimony on Wednesday.

Trump, when asked Friday whether Mueller should testify, deferred to the attorney general.

"I don’t know," he told reporters in the Oval Office. "That’s up to our attorney general, who I think has done a fantastic job."

Barr has said that he would not object to Mueller testifying.

"I have no objection to Bob Mueller personally testifying," he told reporters at a news conference shortly before releasing the special counsel’s report last month.

Barr reiterated that point during his Senate testimony on Wednesday, adding that the White House was not exerting influence on his decision of whether and when to allow Mueller to testify.

White House deputy press secretary Steven Groves said Friday that he’s not aware of any discussions within the West Wing about potential Mueller testimony and that he hasn’t "heard anyone speak out in objection to it."

He suggested the White House counsel would discuss the matter with Trump, who has made clear he has no intention of cooperating with House Democrats' oversight and investigations.

Groves added that it was "premature" to debate the issue since no date had been set for a Mueller hearing.

"There are some questions that I would like to ask him," Groves said. “I mean, he was given a task to either prosecute or decline prosecute, and instead what the American people got for their $30 million were 200 pages of on the one hand this and on the other hand that.

"The question is, does he want to go before Congress and explain his findings and explain his decisionmaking?” he added.

Mike Lillis contributed.