Rep. Steve Cohen Stephen (Steve) Ira CohenTennessee Rep. Steve Cohen wins Democratic primary Democrats exit briefing saying they fear elections under foreign threat Texas Democrat proposes legislation requiring masks in federal facilities MORE (D-Tenn.), a vocal critic of 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, is calling on 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 to resign from the Justice Department in order to "free himself" from 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 "control" and testify before Congress.

"Mueller must resign from 'Justice', free himself of Barr’s control, and explain the #MuellerReport and the truth about Trump and #ObstructionOfJustice," Cohen tweeted Tuesday night.

His call comes hours after reports that Mueller wrote a letter to Barr in late March expressing "frustration" with the way the attorney general detailed the special counsel's conclusions in the investigation into Russia's election interference.

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The Washington Post first broke the story that Mueller had sent the letter, which came days after Barr delivered a four-page memo to Congress in which he stated that the special counsel had not found sufficient evidence of conspiracy between the Trump campaign and Russia. Additionally, Barr said he and Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE determined that the evidence laid out in the Mueller report did not point to President Trump obstructing the special counsel's investigation.

According to the Post, Mueller subsequently sent a letter to Barr stating that the attorney general's memo "did not fully capture the context, nature, and substance of this office’s work and conclusions."

A Justice Department official later confirmed to The Hill that Mueller had "expressed frustration over the lack of context and the resulting media coverage" in his letter to Barr.

The revelation came just a day before Barr is set to answer questions from the Senate Judiciary Committee. At least one Democratic senator, Sen. Chris Van Hollen Christopher (Chris) Van HollenCongress must finish work on popular conservation bill before time runs out Democrats fear Russia interference could spoil bid to retake Senate Mid-Atlantic states sue EPA over Chesapeake Bay pollution MORE of Maryland, has already called on Barr to resign. And key Democratic leaders on Capitol Hill, including Senate Minority Leader Charles Schumer Chuck SchumerCruz blocks amended resolution honoring Ginsburg over language about her dying wish Senate Democrats introduce legislation to probe politicization of pandemic response Schumer interrupted during live briefing by heckler: 'Stop lying to the people' MORE (N.Y.) and 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 (N.Y.), have issued new calls for Mueller to testify.

Cohen has been one of the most vociferous critics of Trump on Capitol Hill, calling the president "the most despicable human being to ever reside in 1600 Pennsylvania Ave.," referring to the White House. He sponsored articles of impeachment against Trump in November 2017.