California has been fighting a court order to release 40,000 prisoners because of its massive overcrowding problem -- a disaster that has led to a court ruling that conditions in said prisons violate Eighth Amendment prohibitions against cruel and unusual punishment because it resulted in a denial of adequate health care. There are about 160,000 inmates in a California prison system designed to house about 84,000 people. As a result, a previous court found that “thousands of inmates suffering from mental illness [were] either undetected, untreated, or both,” and 34 prisoners have actually died because of inadequate care. Sarah Mayeux has a great evaluation of each of the justice's perspectives based on their questions during recent oral arguments before the Supreme Court:
The basic divide that I sensed from the oral argument — I'd be interested to hear if readers reacted differently — was between justices willing to credit the district court's factual findings on the severity of California's overcrowding problem and the connection between overcrowding and sub-constitutional health care (Ginsburg, Breyer, Sotomayor, Kagan, Kennedy), and justices who seemed more skeptical and wanted to fancy themselves common-sense criminological experts (Alito, Scalia), plus Roberts who seemed most concerned with deferring to the state in figuring out what to do.
As Mayeux notes, while the court ordered California to reduce its prison population within two years, the actual window of time during which this became a crisis is at least 15 years, as California simply failed to address the problem despite having previously been ordered to by district courts.
A court order mandating California reduce its prison population is hardly an ideal solution, but it's the direct and predictable result of the American legal system being more punitive than it can afford to be. The way to reduce the prison population is to reduce the number of people you're locking up for long periods of time. As Jacob Sullum points out, 10,000 of the prisoners are serving time merely for drug possession. The conservative wing on the court, absent Kennedy, seems pretty committed to an archaic "tough on crime" mind-set that views pretty much anyone convicted of any crime as a dire threat to public safety.
I'd be remiss, of course, if I didn't mention that Justice Clarence Thomas' "narrow" reading of the Eighth Amendment is that since only judges mete out punishment, “conditions of confinement are not punishment in any recognized sense of the term, unless imposed as part of a sentence.” As far as Thomas is concerned, a prisoner can be "handcuffed to a hitching post and left to stand shirtless in the sun for seven hours without water or bathroom breaks" without having their Eighth Amendment rights violated. So even though he was his usual, silent self, I think we know where he comes down on this.