The 5-4 ruling Monday from the justices come in a classic battle over state versus federal authority, focusing on whether U.S. courts can step in and essentially run state prisons when officials have repeatedly violated basic constitutional guarantees afforded inmates.
The issue came down to a sharply divided debate between public safety concerns and individual rights, a debate that goes into how the three branches of government should balance competing state interests.
The swing vote was Justice Anthony Kennedy, who wrote of the "continuing injury and harm resulting from these serious constitutional violations," including as many as 156,000 people crammed in correctional facilities designed to hold about half that many.
He noted "needless suffering and death have been the well-documented result. Over the whole course of years during which this litigation has been pending, no other remedies have been found to be sufficient."
In dissent, Justice Samuel Alito warned any mass release of inmates to alleviate overcrowding would be "gambling with the safety of the people of California."
The state now has a two-year window to comply, with the clock starting Monday. Officials have not fully explained how their ongoing inmate reduction plan will need to be modified to meet the federal order.
In a statement issued Monday afternoon, California Gov. Jerry Brown said he would take "all steps necessary to protect public safety" in implementing the order.
Brown, a Democrat, signed legislation in April that was aimed at cutting the state's prison population by tens of thousands, largely by housing non-violent felons with sentences less than three years in county jails. In his Monday statement, Brown said the court's ruling recognized that law as "key to meeting this obligation," but said the plan still needs "full and constitutionally guaranteed funding."
Prison overcrowding is a nationwide problem, but California's dilemma is unique in its massive scope and time frame. There is general agreement that the prison conditions across California are disturbing.