AMERICA’S prisons are not for claustrophobes. Since the early 1980s, when harsher sentencing laws were introduced, the number of people incarcerated in the land of the free has increased nearly five-fold—to 2.2m souls. The United States locks up its inhabitants at a rate of 670 per 100,000 people. By contrast, in most European countries, the figures hovers around 100; in Sweden it is 53. New charging guidelines announced on May 12th by Jeff Sessions, Donald Trump’s attorney-general, appear designed to maintain this high incarceration rate—and perhaps to run up the score.

Four years ago, Eric Holder, Barack Obama’s attorney-general between 2009 and 2015, took steps to reduce the rate of imprisonment. Noting that it was “far from sustainable” and that “our system is in too many ways broken”, Mr Holder took aim at the remnants of the "war on drugs" and laws imposing mandatory minimum sentences for low-level drug offences. Mandatory minimums, Mr Holder said, were often “draconian”; prosecutors should crack down hard on violent offenders and steer others to shorter sentences. While “serious, high-level or violent drug traffickers” should plan to spend years behind bars, Mr Holder wrote, “long sentences for low-level, non-violent drug offences do not promote public safety, deterrence and rehabilitation”. Prosecutors should abandon a one-size-fits-all approach and base each charge on an “individualised assessment” of the criminal’s conduct.

That change in priorities is now history. Mr Sessions, touted by Mr Trump for his law-and-order credentials, rescinded Mr Holder’s guidance and replaced it with some instructions of his own. Prosecutors, he wrote, should "charge and pursue the most serious, readily provable offence” in every case. The new policy “affirms our responsibility to enforce the law”, Mr Sessions told his staff; imposing harsh sentences across the board “is moral and just, and produces consistency”. Congress established mandatory floors on prison terms for a reason, he wrote: “By definition, the most serious offences are those that carry the most substantial guidelines sentence, including mandatory minimum sentences”.

Mr Sessions put a curious spin on these changes later in the day. “Charging and sentencing recommendations are bedrock responsibilities of any prosecutor”, he said, and prosecutors “deserve to be un-handcuffed and not micromanaged from Washington”. Yet the memo warns prosecutors not to deviate from the new orders unless they have very good cause. Before opting for a lesser charge, Mr Sessions wrote, “prosecutors should carefully consider whether an exception may be justified” and get the approval of a supervisor. For Thomas Bergstrom, a former US attorney, it seems that “all US attorneys are going to be under the thumb of the attorney-general”. It sounds as if the Department of Justice is opting for a new, much tighter, set of handcuffs for the lawyers who prosecute federal crimes.

What will the decline in prosecutorial discretion mean for America’s prisons? Marc Mauer of The Sentencing Project, a think-tank, says Mr Sessions’ memo “will again fill federal prisons with people convicted of low-level drug offences serving excessive sentences”. Recent efforts to ease overcrowding will be abandoned and Mr Sessions’s change will “exacerbate prison overcrowding, increase spending and jeopardise the safety of staff and prisoners”. Though federal prisons hold fewer inmates than state prisons, a larger percentage of federal inmates are serving time for drug crimes.

Shoving more and more low-level drug violators in prison for long stints may make good sense if the harsher punishments discouraged crime. But the data suggest otherwise. “Research over many decades has demonstrated the deterrent effect of the criminal justice system is a function of the certainty of punishment”, Mr Mauer says, “not its severity”. A 2014 report by the National Research Council surveying several studies on the link between sentence length and crime reduction found that “the deterrent return to increasing already long sentences is modest at best”. Mandatory minimum laws “typically increase already long sentences, which...is not an effective deterrent”.

In a sharp statement on May 12th, Mr Holder condemned Mr Sessions for erasing his four-year-old policy as an “absurd” hold-over of “failed 20th-century ideology”. The “unwise and ill-informed” change is not “tough on crime”, Mr Holder quipped, “it is dumb on crime”. That pithy indictment of Mr Trump’s first major rollback of Obama-era criminal-justice reform will no doubt fall on deaf ears at the White House.