Sen. Dick Durbin Richard (Dick) Joseph DurbinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Grand jury charges no officers in Breonna Taylor death Democrats shoot down talk of expanding Supreme Court MORE (D-Ill.) argued in a Friday Washington Post op-ed that 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 should recuse himself from matters related to 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's investigation.

Durbin argued that Barr's statements and actions since Mueller submitted a final report have put his credibility and independence "in doubt."

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"For that reason, he must recuse himself from any ongoing investigations involving evidence referred by the special counsel’s office," the No. 2 Senate Democrat wrote.

Barr is facing building criticism following this week's release of a letter from Mueller showing the special counsel was dissatisfied with the attorney general's handling of his report on Russian election interference and whether 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 obstructed justice. Mueller accused Barr of creating "public confusion about critical aspects of the results."

Barr angered Democrats further when he refused to appear before a House Judiciary Committee hearing on Thursday, prompting calls for him to be held in contempt or even impeached.

Durbin said Barr's four-page summary of Mueller report and press conference ahead of its redacted release were "over the line" political moves in support of President Trump.

"I don’t know what role Barr thought he was playing on March 24 when he released his four-page summary of Mueller’s report on Russian election interference and when he gave his infamous news conference on April 18," he wrote. "But it is hard to view his actions as anything other than spinning the Mueller report to put Trump in the most politically advantageous light."

"Barr has stepped over the line by politicizing this critical law enforcement investigation to serve the president’s interests," he added.

Durbin also expressed concern about 14 instances of evidence of potential criminal activity that were outside the special counsel's scope, which were then referred to other parts of the Justice Department, per the report.

"Barr has repeatedly proved he should have no hand in any of them," he wrote. "For the sake of the rule of law and to make sure these investigations are carried out independent of political considerations, he must recuse."

The Hill has reached out to the Justice Department for comment.

Barr was asked when he testified before Congress Wednesday if he would recuse himself from any further cases related to the Mueller investigation, and he said he would not.

Durbin's opinion piece follows calls from several lawmakers for the the Justice Department's inspector general to look into Barr's handling of Mueller's report. A chorus of Democrats have also called for his resignation.

Barr's predecessor Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE recused himself from the Russia investigation, which became a serious point of contention between him and Trump, particularly after the appointment of the special counsel.