Prompted in part by that report, the Justice Department initiated a review of thousands of cases involving microscopic matching of hair samples. In 2015, the F.B.I. announced its shocking initial findings: In 96 percent of cases, analysts gave erroneous testimony. At a meeting last spring of the commission that Mr. Sessions just disbanded, the department said it would expand the view to include a wider array of forensic disciplines.

With the announcement by Mr. Sessions, this momentum comes to a screeching halt. Although forensic science would seem a low priority for an incoming attorney general, it is not altogether surprising that it was in Mr. Sessions’s sights. As a senator (and former prosecutor), Mr. Sessions made forensic science a priority. He sponsored and shepherded to passage the Paul Coverdell National Forensic Science Improvement Act of 2000, which remains the signature federal funding mechanism for state all-purpose forensic labs. That might suggest that Mr. Sessions would care about the integrity of forensic science, but his enthusiasm has been for more — not better — forensic evidence. When the National Academy of Sciences’ scathing report was released, Senator Sessions simply waved it away, remarking, “I don’t think we should suggest that those proven scientific principles that we’ve been using for decades are somehow uncertain” — ignoring the panel of experts who had concluded just that.

Every independent critique of our forensic science system comes back to the same basic conclusion about both the root of the problem and how to fix it: Forensic science rests under the exclusive control of police and prosecutors, and its legitimacy and integrity have suffered as a result. Even Obama-era law enforcement officials had a tenuous relationship to reform. Just last year, the President’s Council of Advisors on Science and Technology issued a report that reaffirmed and extended the 2009 findings. The F.B.I.’s response was to vehemently disagree, the Obama Department of Justice basically replied, “Thanks, no thanks,” and the professional association for the nation’s district attorneys criticized the report for its insufficient attention to “the ancient debate over precisely what constitutes ‘science’ ” while asserting that the final arbiter of good science should be lawyers and courtrooms, not scientists and laboratories.

The 2009 report concluded that the only way to ensure effective oversight of forensic evidence was to protect its independence from law enforcement. But its recommendation of a national, independent oversight agency was met with intense resistance from federal and state law enforcement. Instead, the national commission was formed as a compromise solution that brought in the National Institute on Standards and Technology as co-chairs and stewards of scientific values. Some forensic scientists — at times grudging partners in the process of reform — even came to embrace greater professionalization, and one major professional organization recently declined to support the Justice Department’s proposal to move forensics in-house.

The loss of an even partially independent national commission is no trivial matter.

In its brief two years of existence, it drafted 43 standards that actually changed forensic science, on the ground, for the better. The commission’s guidance covered issues like certification requirements for forensic examiners (who, unlike your local manicurist or food server, typically must not pass any basic competency exams still), discovery rules (providing criminal defendants with at least some of what parties receive in civil cases) and reporting standards (discouraging the use of the popular phrase “reasonable degree of scientific certainty” as it has “no scientific meaning and may mislead fact-finders”). The National Commission on Forensic Science was even poised to issue a raft of best practices for the wild west of digital forensics, which has exploded without supervision over the years. It seemed that a promising new era of accuracy, transparency and accountability in forensic science had dawned.