THE MORE one looks at Attorney General William P. Barr’s move to drop charges against Trump crony Michael Flynn, the more corrupt it appears. That is the upshot of a bracingly candid analysis from John Gleeson, a former federal judge the court appointed to assess Mr. Barr’s effort to let Mr. Flynn off, which emerged Wednesday.

Mr. Barr’s Justice Department is engaged in “an unconvincing effort to disguise as legitimate a decision to dismiss that is based solely on the fact that Flynn is a political ally of President Trump,” Mr. Gleeson wrote. “Even bending every inference in the Government’s favor, its filing here falls short.”

Mr. Gleeson is not the first legal expert to criticize Mr. Barr. But he is not just an idle commentator or partisan litigator. Moreover, his analysis is detailed, meticulous — and, because Mr. Barr’s decision was so egregious, unusually damning.

Mr. Flynn pleaded guilty in 2017 to lying to FBI investigators, a felony, as they scrutinized his interactions with Russian then-Ambassador Sergey Kislyak. The former national security adviser later renounced his guilty plea and accused the government of manipulating him. The Justice Department did not buy his arguments — until Mr. Barr got involved. The attorney general ordered last month that the Flynn charges be dropped, on the grounds that Mr. Flynn’s lies to the FBI were immaterial to the agency’s work and therefore excusable.

Only a contorted view of the case could justify such a conclusion. “Pursuant to an active investigation into whether President Trump’s campaign officials coordinated activities with the Government of Russia, one of those officials lied to the FBI about coordinating activities with the Government of Russia,” Mr. Gleeson wrote. “It is hard to conceive of a more material false statement than this one.”

The former judge noted that FBI officials might have asked a variety of follow-up questions if Mr. Flynn had answered truthfully, and that the fact of Mr. Flynn’s repeated lies itself carried national security implications.

Mr. Barr appears to believe that Mr. Flynn’s prosecution — and, indeed, the entire Russia investigation — reflected a partisan effort to kneecap a Republican president. In fact, Mr. Gleeson cited example after example of cases in which the Justice Department made arguments diametrically opposite to those Mr. Barr advanced to justify clearing Mr. Flynn — cases that involved defendants who were not the president’s friends.

Mr. Gleeson concludes that “the Government may not enlist a court in dismissing a case solely because the defendant is a friend and political ally of the President — and where the ostensible reasons advanced for dismissal amount to a thin and unpersuasive disguise.”

U.S. District Court Judge Emmet G. Sullivan, who presides over the Flynn case, is not required to approve Mr. Barr’s request to drop the charges. He should refuse. And the U.S. Court of Appeals for the District of Columbia Circuit, which has itself become involved, should allow Mr. Sullivan to exercise his discretion. This is one of the rare cases in which prosecutors’ behavior is so egregious that they deserve none of the usual respect and deference.

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