Holder’s changes addressed longstanding criticisms of the federal posture toward drug crimes. “In some cases, mandatory-minimum and recidivist-enhancement statutes have resulted in unduly harsh sentences and perceived or actual disparities that do not reflect our Principles of Federal Prosecution,” he wrote at the time. “Long sentences for low-level, non-violent drug offenses do not promote public safety, deterrence, and rehabilitation.”

To that end, he instructed prosecutors not to list the quantity of drugs seized when charging a defendant unless he or she was “an organizer, leader, manager, or supervisor of others within a criminal organization,” had used violence, or had a lengthy criminal history. Prosecutors should also consider, he said, if their charges “would create a gross sentencing disparity” compared with other defendants.

Sessions’s new memo effectively rejects that stance, insisting on seeking the maximum punishments lawfully possible. “Prosecutors must disclose to the sentencing court all facts that impact the sentencing guidelines or mandatory-minimum sentences, and should in all cases seek a reasonable sentence under the factors” prescribed by federal drug laws, he wrote. Any deviations from the policy require “supervisory approval” from the Justice Department.

In a statement shortly after Sessions’s memo was issued, Holder castigated his successor’s move. “The policy announced today is not tough on crime,” he said. “It is dumb on crime. It is an ideologically motivated, cookie-cutter approach that has only been proven to generate unfairly long sentences that are often applied indiscriminately and do little to achieve long-term public safety.”

Monday’s “absurd reversal,” Holder added, “is driven by voices who have not only been discredited but until now have been relegated to the fringes of this debate.”

The shift underscores the central role prosecutors play when determining how long Americans spend behind bars. Prosecutorial discretion, like gravity, is the unseen force that binds the American criminal-justice system together. Federal prosecutors have a broad array of legal mechanisms at their disposal with which they can ratchet a defendant’s punishment higher or lower, depending on which charges they file and which sentencing enhancements they seek. Roughly 95 percent of federal criminal cases are resolved through plea deals, making the prosecutor the most influential actor in the modern system.

It also highlights the influence of Sessions, one of President Trump’s earliest high-profile supporters, in shaping the administration’s stance on criminal-justice issues. Rolling back Justice Department policies to a more draconian era wouldn’t be a surprising move for the former Alabama senator. As policing and justice issues rose to the forefront of the national conversation in recent years, Sessions became a frequent critic of reform efforts, including federal oversight of local law enforcement. He also played a prominent role in scuttling a bipartisan sentencing-reform bill in the Senate last year that had the support of figures ranging from Barack Obama to the Koch brothers.