Last week, the DOJ moved to drop charges against Flynn who had pleaded guilty twice to lying to the FBI about his contacts with the former Russian ambassador during the presidential transition.
"Attorney General Barr’s repeated actions to use the Department as a tool to further President Trump’s personal and political interests have undermined any claim to the deference that courts usually apply to the Department’s decisions about whether or not to prosecute a case," reads the letter, which was organized by the group 'Protect Democracy'.
Barr, in a CBS News interview last week, denied he was acting at the president's behest in his support of the move to drop the charges against Flynn.
The federal judge in the case as of Monday morning had not yet responded to the DOJ filing.
The letter is the latest in a wave of backlash among former officials to the DOJ's surprise reversal in the Flynn case.
Barr has said he supported dropping the charges based on a recommendation from the U.S. attorney from the Eastern District of Missouri Jeffrey Jensen, who was tasked by Barr with reviewing how FBI agents handled their interview of Flynn at the White House in January 2017.
The filing last Thursday by the U.S. Attorney in D.C. Timothy Shea cited new evidence uncovered in Jensen's review that the department said rendered the investigation into Flynn illegitimate at the time of his interview.
Mary McCord, who served as the former acting assistant Attorney General for National Security during the early stages of the Russia investigation, said in a New York Times op-ed Sunday that the DOJ's filing to dismiss the charges cited comments she made in an interview "more than 25 times."
McCord accused the department of "twisting" her comments in a misleading effort to undercut the department's case against Flynn.
"The report of my interview is no support for Mr. Barr’s dismissal of the Flynn case," McCord said. "It does not suggest that the F.B.I. had no counterintelligence reason for investigating Mr. Flynn. It does not suggest that the F.B.I.’s interview of Mr. Flynn — which led to the false-statements charge — was unlawful or unjustified."
McCord did note, however, that she had been critical of the FBI for failing to properly consult the Justice Department of its agents' plans to interview Flynn until when they were already "on the way" to the White House.
"There were protocols for engaging with White House officials and protocols for interviews, and this was, of course, a sensitive situation,” McCord said in the op-ed, while adding, "the report of my interview does not anywhere suggest that the F.B.I.’s interview of Mr. Flynn was unconstitutional, unlawful or not “tethered” to any legitimate counterintelligence purpose."
Separately, a former career prosecutor who resigned from the department after Barr's intervention in the sentencing of former Trump ally Roger Stone broke his silence Monday in a Washington Post op-ed, describing the move as the latest "appalling chapter" in the politicization of the nation's top law enforcement agency.
"The dedicated public servants who remain cannot respond publicly to those who claim that the department acted appropriately in these cases," said Jonathan Kravis, who now works in the office of D.C. attorney general Karl Racine. "But I can, and I say this. If the department truly acted because of good-faith commitments to legal positions, then where is the evidence of those commitments in other cases that do not involve friends of the president?"
In an interview last week, Barr said he was "prepared" for the criticism that would likely follow his decision in the Flynn case.
"I also think it's sad that nowadays these partisan feelings are so strong that people have lost any sense of justice," Barr told CBS. "And the groups that usually worry about civil liberties and making sure that there's proper procedures followed and standards set seem to be ignoring it and willing to destroy people's lives and see great injustices done."