When the Supreme Court revived capital punishment in 1976, just four years after de facto abolishing it, the justices effectively took ownership of the American death penalty and all its outcomes. They have spent the decades since then setting its legal and constitutional parameters, supervising its general implementation, sanctioning its use in specific cases, and brushing aside concerns about its many flaws.

That unusual role in the American legal system is about to change. With Justice Anthony Kennedy’s retirement from the court this summer, the Supreme Court will lose a heterodox jurist whose willingness to cross ideological divides made him the deciding factor in many legal battles. In cases involving the Eighth Amendment’s prohibition against cruel and unusual punishment, his judgment often meant the difference between life and death for hundreds of death-row prisoners.

“In a very real sense, the Eighth Amendment meant whatever Justice Kennedy decided that it meant,” Robert Dunham, the executive director of the Death Penalty Information Center, told me. “He was often the fifth vote in denying stays of execution and in favoring the state on questions of lethal injection, but he was also often a fifth vote for determining that a particular death-penalty practice was unconstitutional.”

The high court will likely continue to intervene in death-penalty cases that stray too far from the legal mainstream. But without Kennedy, it will no longer be the venue for a systemic attack on capital punishment as it had been in recent years. “It seems likely that there will be a firm, five-person majority on the court in Kennedy’s wake with absolutely no interest in revisiting the status quo on the constitutionality of capital punishment,” Carol Steiker, a Harvard University law professor who specializes in the death penalty, told me.

Kennedy first joined the court in 1988, but he didn’t make his mark on capital cases until after he had spent more than a decade there. In the 2002 case Atkins v. Virginia, he joined the majority decision that barred states from executing people with intellectual disabilities. Three years later, Kennedy wrote the court’s opinion in Roper v. Simmons to abolish the death penalty for crimes committed when the defendant was under 18 years of age. Roper’s logic later became instrumental in the court’s rulings that radically scaled back life-without-parole sentences for juvenile offenders.

In each case, Kennedy’s stance drew strenuous dissents from the court’s other conservatives. After Kennedy concluded in Roper that executing people for crimes they committed as juveniles no longer fit within the nation’s “evolving standards of decency,” noting that the United States was the last country on Earth that still permitted the practice, Justice Antonin Scalia complained, “The court thus proclaims itself sole arbiter of our nation’s moral standards—and in the course of discharging that awesome responsibility purports to take guidance from the views of foreign courts and legislatures.”

In 2008, Kennedy joined again with the court’s four liberal justices in Kennedy v. Louisiana to abolish the death penalty for crimes other than murder. The case at hand involved a particularly disturbing case of child rape, and the dissenting justices criticized the court for deciding such acts were beyond the death penalty’s scope. “I have little doubt that, in the eyes of ordinary Americans, the very worst child rapists—predators who seek out and inflict serious physical and emotional injury on defenseless young children—are the epitome of moral depravity,” Justice Samuel Alito wrote.

Kennedy nonetheless drew a line between crimes in which the victim died and those in which they did not. “In this context, which involves a crime that in many cases will overwhelm a decent person’s judgment, we have no confidence that the imposition of the death penalty would not be so arbitrary as to be ‘freakish,’” he wrote, paraphrasing a death-penalty ruling from the 1970s. “We cannot sanction this result when the harm to the victim, though grave, cannot be quantified in the same way as death of the victim.”

Those decisions represented “the biggest area of Eighth Amendment growth in a protective direction in the last two decades, and Kennedy was instrumental in, if not the chief architect of, that growth,” Carol Steiker, a Harvard University law professor who specializes in the death penalty, told me. “The jurisprudence that he helped develop and build in those cases is probably the best, most likely path to constitutional abolition.”

In the 2015 case Glossip v. Gross, Kennedy joined the court’s other conservatives to uphold Oklahoma’s haphazard lethal-injection protocol. But there were indications of movement toward abolition behind the scenes. Justice Stephen Breyer wrote a lengthy dissent in Glossip that called for the court to reconsider whether the death penalty violated the Eighth Amendment, the first such call from a sitting justice in almost a decade. A few months later, Scalia told a University of Minnesota law school audience that he wouldn’t be surprised if the court voted to abolish it soon.

Some death-penalty abolitionists and legal observers took these as signals that the court—Kennedy himself, for all intents and purposes—might declare capital punishment unconstitutional, if given the opportunity. In the years that followed, capital litigators brought multiple appeals to the justices that asked them to revisit the practice’s constitutionality in hopes of triggering such a ruling. But the court declined to hear all of them, suggesting that its most influential member wasn’t willing to go that far.

With Kennedy now gone, it’s virtually certain that the Supreme Court won’t abolish the death penalty for at least a generation. Earlier this month, President Donald Trump nominated Brett Kavanaugh, a reliably conservative judge on the D.C. Circuit Court of Appeals, to fill Kennedy’s seat. While Trump himself is an unusually enthusiastic proponent of the practice, Kavanaugh’s own views on the death penalty are unknown. The D.C. Circuit’s narrow geographic jurisdiction means that it almost never hears death-penalty cases compared to the other federal appellate circuits.

As a result, there is no clear record for how Kavanaugh approaches the practice as a judge. Justices Clarence Thomas and Samuel Alito are resistant to curtailing capital punishment, and Justice Neil Gorsuch has voted alongside them during his first term on the court. If Kavanaugh votes in a similar manner, the court’s posture toward the death penalty would shift decisively away from limiting its scope. “The immediate impact of Kennedy’s retirement in terms of Eighth Amendment law is that it’s now whatever Chief Justice Roberts decides that it is,” Dunham said.

Roberts generally sides with the rest of the court’s conservatives on death-penalty matters. He has also joined the court’s liberals on occasion to rule in favor of defendants in certain egregious cases. In the 2017 case Buck v. Davis, he sided with a death-row prisoner after an expert testified during the sentencing phase that he posed a greater threat of “future dangerousness” because he is black. Though the exchange was a brief part of the overall trial, Roberts said in his majority opinion that it was still too much. “Some toxins are deadly in small doses,” he wrote.

Death-row prisoners will still bring cases to the Supreme Court, but Steiker said that the future of abolition efforts will now turn to the state and local level. “States are really where the story is happening,” she told me. “There are state constitutional challenges that can be brought. Seven state legislatures have voted to abolish the death penalty in the past ten or twelve years.” She also noted that a growing number of district attorneys are declining to seek the death penalty in cases where they otherwise could.

A local focus makes sense given the current geography of capital punishment. Death sentences increasingly come from only a handful of counties scattered across the country. Though state legislatures allow or forbid the death penalty as a matter of law, local prosecutors often decide in practice whether a defendant will face it. Cities like Houston and Philadelphia that once handed down dozens of death sentences have recently seen the election of district attorneys who are more skeptical of it.

For now, the rulings written by Kennedy will continue to mark the outer limits for American executions on a national level—unless the justices of a future generation choose to push them even further. “The law that Justice Kennedy leaves behind offers something of a blueprint for a future Supreme Court if it wanted to continue this project of reassessing the death penalty and its concordance—or not—with evolving standards of decency,” Steiker said.