Nine Democrat senators sent a letter on Friday to Attorney General William Barr, urging him to resign immediately for overruling the sentencing recommendation of seven to nine years in prison for 67-year-old Roger Stone, President Donald Trump’s longtime confidant.

In the letter sent to the AG, the Democrat lawmakers wrote:

The interference in this case by you or other senior DOJ officials working under you is a clear violation of your duty to defend fair, impartial, and equal justice for all Americans.

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It appears to show that you and other top DOJ officials intervened in a clearly political fashion to undermine the administration of justice at the President’s behest in order to protect a well-connected political ally who committed a “direct and brazen attack on the rule of law.”

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The shocking actions taken by you or your senior staff to seek special protections for Mr. Stone make a mockery of your responsibilities to seek equal justice under the law and reveal that you are unfit to head the DOJ. A DOJ that abandons the rule of law in order to give sweetheart deals to criminals acting on behalf of the President of the United States is as corrupt as it is unacceptable.

Several news outlets have quoted from the letter, posted on Twitter by Frank Thorp from NBC News.

Democrat Sens. Elizabeth Warren (MA), Richard Blumenthal (CT), Ed Markey (MA), Patty Murray (WA), Jeff Merkley (OR), Chris Van Hollen (MD), Ron Wyden (OR), Bernie Sanders (VT), and Mazie Hirono (HI) signed the letter. Warren and Sanders are running for president.

Under Barr’s leadership, the U.S. Department of Justice (DOJ) made plans to recommend a lighter sentence for Stone.

A federal court convicted Stone for obstructing a congressional investigation, making false statements to investigators, and tampering with witnesses in connection to the Russian collusion hoax probe by special counsel Robert Mueller.

Barr’s decision prompted the four prosecutors who made the sentencing recommendation to withdraw from the case or resign from DOJ altogether.

The attorney general’s move also drew the ire of Democrats who have demanded an investigation of DOJ’s decision. Republicans, who currently control the Senate, have dismissed the Democrats’ demands.

Some GOP senators and Barr, however, have criticized Trump for lambasting the original sentencing request via Twitter.

In a recent interview with ABC News, Barr asserted that he decided to recommend a lower sentence for Stone before Trump’s criticism of the prosecutors’ request came to light.

Barr conceded during the interview that the president’s tweets are making his job “impossible.”