For the fourth time in as many years, the Supreme Court on Thursday considered exactly what kind of violent crimes call for the mandatory prison terms Congress provided in the Armed Career Criminal Act.

Get used to it, Justice Antonin Scalia said in a sharp-edged dissent; the court will be trying to sort out the law’s meaning “until the cows come home.”

The justices said that fleeing police custody in a vehicle could be a “violent felony” under the law’s definitions. Scalia not only criticized that decision, but the Congress that approved a law that contains provisions he considers so vague as to be unconsititutional.

“Fuzzy, leave-the-details-to-be-sorted-out-by-the-courts legislation is attractive to the Congressman who wants credit for addressing a national problem but does not have the time (or perhaps the votes) to grapple with the nitty-gritty,” Scalia wrote. “In the field of criminal law, at least, it is time to call a halt.”

Justice Anthony M. Kennedy acknowledged that Congress was not precise in enumerating all of the violent offenses under the ACCA, which contains a mandatory minimum sentence of 15 years for an armed defendant who has three prior convictions for violent felonies.

“Although this approach may at times be more difficult for courts to implement, it is within congressional power to enact,” Kennedy said.

Sykes v. U.S. resulted in a decision that blurred the court’s usual ideological lines. Kennedy was joined by Chief Justice John G. Roberts Jr. and Justices Stephen G. Breyer, Samuel A. Alito Jr. and Sonia Sotomayor. Justice Clarence Thomas agreed with the outcome, but not the majority’s reasoning.

Justice Elena Kagan dissented in an opinion joined by Justice Ruth Bader Ginsburg. Scalia objected alone.

Under the ACCA, when punishable by prison terms of more than one year, burglary, arson, extortion and crimes that involve the use of explosives are considered violent felonies. But under the act’s “residual” provision, so is unspecified conduct that “presents a serious potential risk of physical injury to another.”

In the case at hand, Marcus Sykes faced the ACCA’s heightened penalties when he pleaded guilty to possessing a firearm in an attempted robbery of two people. He had previously been convicted of two armed robberies and of violating an Indiana law by fleeing in a vehicle after a police officer ordered him to stop.

He argued that vehicle flight, though a felony, is not a violent felony. The U.S. Court of Appeals for the 7th Circuit disagreed, but the question has divided other appellate courts.

Kennedy said vehicle flight can be compared to other crimes on the list Congress provided. “When a perpetrator defies a law enforcement command by fleeing in a car, the determination to elude capture makes a lack of concern for the safety of property and persons of pedestrians and other drivers an inherent part of the offense,” he said.

Thomas agreed, although he thought the majority used the wrong test in making its decision.

Kagan and Ginsburg noted that Sykes was convicted under the least severe of Indiana’s vehicle-flight offenses. It “lacks any element relating to threat of physical injury,” Kagan wrote.

Scalia washed his hands of the court’s “tutti-frutti” decision and said it should declare the residual clause unconstitutional instead of continually attempting to define it.

“Insanity, it has been said, is doing the same thing over and over again, but expecting different results,” he wrote. “We should admit that ACCA’s residual provision is a drafting failure.”

In a second criminal case, the court unanimously agreed that a federal law that imposes tough penalties for cocaine possession includes other forms of “cocaine base” than just crack cocaine.

Lower courts had been divided on how to interpret the law.

The case is DePierre v. U.S .