When does the execution of a prisoner cross a line and become “cruel and unusual”? In the strange world of the US death penalty, that is an all-important legal question. The US constitution prohibits “cruel and unusual” punishments, but condemned prisoners seeking relief have to prove their executions meet this definition, as opposed to just being “painful”.

This week the US supreme court handed down a ruling that sought to clarify what manner of execution would meet constitutional standards of cruelty and unusualness. The court’s answer? Disembowelling.

Not only disembowelling: the conservative justices in the majority conceded that public dissection and burning alive would also be too much. In doing so, they cited the definition of cruelty given in Dr Samuel Johnson’s Dictionary of the English Language – specifically its fourth edition, published in 1773.

The court’s ruling came in response to an appeal filed by a condemned prisoner, Russell Bucklew, who has a rare medical condition that causes blood-filled tumours to grow in his head. Doctors had told him lethal injection would cause those tumours to burst and lead him to suffocate on his own blood, so he sought to be executed using nitrogen gas instead.

The court denied Bucklew’s request, finding that he had not been specific enough about whether his executioners should use “a gas chamber, a tent, a hood, a mask, or some other delivery device”.

The court’s ruling confirms a legal standard established in a 2015 case, under which prisoners seeking to challenge a torturous lethal injection must present a suitable alternative way for the state to execute them. Incidentally, no judge has yet ruled it cruel or unusual to force prisoners into choosing their own method of execution.

It also recalls one of the most quoted statements in the body’s history: the 1994 pledge by Justice Harry Blackmun that “from this day forward, I no longer shall tinker with the machinery of death”.

This kind of tinkering is the court’s current preoccupation. How else might we characterise a ruling that carefully considers the relative benefits of disembowelling, dissection, gassing and hanging – the latter a method that new justice Neil Gorsuch suggested might not be unconstitutional on the basis that it was never intended to cause pain?

Monday’s ruling was delivered by the supreme court’s new conservative majority: the majority opinion was written by Gorsuch, and endorsed by Brett Kavanaugh.

But while it may tell us a lot about the current court, it does not reflect the reality of capital punishment in the US today. While the justices’ deliberations might suggest a resurgence in US executions, in fact the opposite is true.

The latest annual report by the Death Penalty Information Center found death sentences and executions in the United States to be “near generational lows”, with most death sentences coming from just four states: Texas, Florida, Ohio and California.

Even in these states, the death penalty is dying. Last month, the governor of California, Gavin Newsom, announced a moratorium on executions: “Our death penalty system has been – by any measure – a failure,” he said.

Rejecting the perverse misuse of medicines in lethal injections, pharmaceutical companies across the board refuse to sell their drugs for capital punishment, making publicly clear their products are made to save and improve lives, not to end them in torturous executions.

Politicians of all persuasions have also turned against capital punishment. This year, New Hampshire’s house of representatives passed a death penalty repeal bill with a majority large enough to override a veto threatened by the state’s governor. Elsewhere, bills to abolish or restrict the death penalty have advanced under conservative stewardship in states including Wyoming and Kentucky.

In this respect, the image that defines the US death penalty in 2019 may not be nine robed justices weighing up execution methods. A more powerful picture, and one of greater consequence, is the dismantling of the execution chamber at California’s San Quentin state prison – a sight evoking 737 executions of people currently on the state’s death row that, for now, will not be carried out.

The life or death of capital punishment will not be determined solely in the chamber of the supreme court. Voters, politicians and businesses also have a say. And, from California to New Hampshire, voices are rising against further tinkering with the machinery of death.

• Maya Foa is director of Reprieve