ATTORNEY GENERAL William P. Barr entered office with more credibility than many Trump appointees. A veteran of the George H.W. Bush administration, Mr. Barr avowed loyalty to the Justice Department’s mission and, nearing the end of his career, seemed to have little incentive to serve as another Trump sycophant. Yet Mr. Barr has lit his reputation on fire, and he just added more fuel in his Wednesday testimony before a Senate panel.

Much of the hearing centered on the attorney general’s decision to release a highly misleading representation of the findings of special counsel Robert S. Mueller III’s Russia investigation. In particular, Mr. Barr failed to acknowledge the alarming nature of Mr. Mueller’s analysis on whether President Trump obstructed justice, and he did not explain why the special counsel declined to say whether Mr. Trump was guilty of the charge. This really matters: Given the damning account in Mr. Mueller’s report, what appeared to be keeping the special counsel from accusing the president of criminal acts was not the lack of evidence but the fact that the president cannot be charged under Justice Department rules.

Mr. Barr defended himself Wednesday by insisting that his memo, publicized weeks before he released any additional material, was technically accurate, despite the fact that his spin deeply affected the reception of Mr. Mueller’s full report when the public finally got it. It was not supposed to be a full summary of the special counsel’s report, he insisted — just a brief explanation of the top-line conclusions. Mr. Barr’s long history in Washington belies his argument: He should have known how his pre-spinning of the Mueller report would distort the truth of the special counsel’s damning findings, to the president’s benefit. He did it anyway.