Richard Wolf

USA TODAY

WASHINGTON -- The death penalty sharply divided the Supreme Court Tuesday as it has done for decades, but a slim majority of justices appeared likely to block Texas from executing a man under an outdated definition of intellectual disability.

It was the third death penalty case to reach the court in its new term, with several others lined up for possible consideration. Each challenge presents a different issue, ranging from overzealous prosecutors and ineffective defense lawyers to execution methods and innocence claims.

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The latest case concerned Texas' unique system for deciding who is intellectually disabled, one that is not based on the latest clinical guidelines. While three conservative justices seemed likely to grant the state discretion, five others indicated their disapproval.

By allowing one state to define mental impairment differently than another, Justice Ruth Bader Ginsburg said, "You're opening the door to inconsistent results ... something that we try to prevent from happening in capital cases."

Justice Stephen Breyer — who, with Ginsburg's support, suggested last year that the high court consider declaring capital punishment unconstitutional — said the Texas standard "would free some, while subjecting others to the death penalty."

The key vote will come from Justice Anthony Kennedy, the lone conservative to voice skepticism about the Texas system. While acknowledging that the Supreme Court's 2002 precedent barring execution of the intellectually disabled "left some discretion to the states," he said Texas' method of determining disability seemed designed to limit who can claim it.

That left Chief Justice John Roberts and Justice Samuel Alito on the other side — presumably along with Justice Clarence Thomas, who did not speak during the hour-long oral argument.

Alito noted that Texas' method of judging a defendant's abilities along with his deficits is backed by some experts in the field. "Are these quacks?" he asked Clifford Sloan, the lawyer representing death row inmate Bobby James Moore.

Texas Solicitor General Scott Keller said the state goes by the Supreme Court's standard, looking at defendants' intellectual functioning, adaptive behaviors and the age of onset for mental impairments. "Texas is well within the national consensus," he said.

Not so, Sloan argued. "Texas is very extreme and stands alone," he said, accusing the state of using "lay stereotypes" of intellectual disability such as the character Lennie in John Steinbeck's "Of Mice and Men."

Moore's case dates back to 1980, when he shot and killed a grocery store clerk during a botched robbery. His attorneys say his mental competency was gauged using a 23-year-old definition of intellectual disability, rather than current medical standards.

The court has tightened sentencing rules for people with intellectual disabilities since its landmark 2002 ruling in Atkins v. Virginia. In 2014, it barred Florida from using a single, strict IQ standard to determine a prisoner's competency.

Texas leads the nation in executions with 538 since 1976, nearly five times the total of any other state. Its effort to execute another prisoner despite racially biased testimony from a defense witness was heard by the high court last month.

Nationwide, the pace of executions has slowed since peaking in 1999. This year there will be about 20, the lowest number in a quarter century. That's a result of action by legislatures and courts, as well as problems states face getting the drugs required for lethal injections.

Despite that trend, voters in California, Nebraska and Oklahoma decided to retain or restore capital punishment at the polls this month.