“Research still confirms what this Court suggested over a century ago: Years on end of near-total isolation exacts a terrible price,” he summarized.

Kennedy’s critique of solitary confinement in Davis came without warning or fanfare. Davis was not a case about solitary confinement at all; the Court had accepted it to address peremptory challenges during jury selection. But the length and condition of Ayala’s imprisonment appears to have caught Kennedy’s attention. Towards the end of oral arguments on March 3, he briefly quizzed Anthony Dain, Ayala’s lawyer, for more details.

“This crime was, what, 30 years ago and the trial [was] 26 years ago? Has he spent time in solitary confinement, and if so, how much?” Kennedy asked.

“He has spent his entire time in what’s called administrative segregation. When I visit him, I visit him through glass and wire bars,” Dain replied. When the justice inquired about the difference between solitary confinement and administrative segregation, Dain said his client spent 23 hours in his cell and was allowed one hour of activity.

“One hour,” Kennedy muttered in response as Dain’s time expired.

Solitary confinement is a new battleground for the Court’s second-longest serving justice, but not a surprising one. Few justices on the Supreme Court have wielded the Eighth Amendment as expansively as Anthony Kennedy. On the death penalty, he wrote the majority opinions in Roper v. Simmons, which forbade the execution of juvenile offenders, and Kennedy v. Louisiana, which struck down death sentences for non-homicide crimes. In 2011, he joined with the Court’s liberal wing in Brown v. Plata to uphold a landmark federal-court order requiring California to reduce prison overcrowding. Kennedy also provided the fifth vote in Miller v. Alabama, in which the Court struck down mandatory life-without-parole sentences for juveniles in 2012. As the court’s swing vote, he carries tremendous power to shape cases to form majorities.

Although Kennedy addressed solitary confinement specifically, he also invoked mass incarceration in general and the national debate surrounding it. “There are indications of a new and growing awareness in the broader public of the subject of corrections and of solitary confinement in particular,” he noted. Perhaps hoping to reach this broader public, Kennedy wrote without dense legal jargon and cited examples ranging from Kalief Browder to Dr. Manette, the imprisoned father of Lucie in Charles Dickens’s A Tale of Two Cities. “Even Manette, while imprisoned, had a work bench and tools to make shoes, a type of diversion no doubt denied many of today’s inmates,” he observed.

But Kennedy’s concurrence also seemed to be directed toward the American legal community, whose disengagement from prison issues he has previously lamented. “In law school, I never heard about corrections,” he told a congressional hearing on March 23, two weeks after the Davis oral arguments. “Lawyers are fascinated with the guilt/innocence adjudication process. Once [it] is over, we have no interest in corrections. Doctors and psychiatrists know more about the corrections system than we do.”