When a judge sentences a 13-year-old boy to spend the rest of his life in prison without a chance of parole for a crime in which nobody has died, is he meting out justice? Or is he acting as society's cop?

That question was looming in the background Monday as the U.S. Supreme Court prepared to hear two cases in which two Florida boys — a 13-year-old rapist and a 17-year-old repeat offender with a predilection for armed robbery — got the same punishment: life without parole.

The court will decide whether sentencing the teens to life for less than murder constitutes "cruel and unusual punishment," which is prohibited by the Eighth Amendment to the Constitution. But the cases will also fuel questions about the role and power of American judges.

In both cases the judges ruled in large part to protect citizens from future crimes, prompting critics to say that they used their gavels to police society, and not just to administer law.

Florida, like most states, allows judges to impose life sentences without parole for juveniles even when the crime does not result in a victim's death.

"I think the judge in a case like this is acting within the authority delegated to him within the [state] legislature," former Supreme Court nominee Robert Bork told FoxNews.com.

On the issue of ruling with the intent to protect society from future crimes, Bork said, "Apparently the legislature authorized them to rule with things like that in mind, so I assume that's a core function of criminal law and what the legislature must have intended — that a judge should consider that function of a criminal law in imposing that sentence."

In one of the cases, Graham v. Florida, Terrance Graham was 17-years-old and on parole when he broke into a man's home and robbed him at gunpoint. Graham pleaded guilty to armed burglary and was sent to prison for the rest of his life. The judge who imposed the sentence concluded that Graham had wasted his second chance at freedom and was a significant threat to society.

In the other case, Sullivan v. Florida, Joe Sullivan was sentenced to life without parole for raping an elderly woman in 1989, when he was 13-year-old.

Graham, now 22, and Sullivan, now 33, are being held in Florida prisons, which house more than 70 percent of juvenile defendants serving life sentences without chance of parole for crimes other than homicide.

Lawyers for the defendants in both cases cite the Supreme Court's 2005 ruling in Roper v. Simmons, in which the high court ruled 5-4 that a death sentence for someone younger than 18 constitutes cruel and unusual punishment and therefore violates the Eighth Amendment.

Graham's attorneys say the court's reasoning in Roper v. Simmons should extend to their client. The defense claims that like the mentally disabled, juveniles are "categorically less culpable than the average criminal," and that when compared to adults, juveniles "cannot with reliability be classified among the worst offenders."

But the state has said that the severity of Graham's sentence was "not grossly disproportionate to [the] violent crimes against [his] vulnerable victims." The state also claims Graham's crime was so severe that even he did not challenge his treatment as an adult offender.

Lawyers for Sullivan have also cited the Roper case, saying the high court should declare that a life sentence for a 13-year-old constitutes cruel and unusual punishment. The defense has argued that such a sentence imposed on teenagers is unjust because they are "unfinished products, human works-in-progress."

The life sentences imposed by both Florida judges have also raised questions over the role of the judges themselves. Supporters of the sentences say the role of the courts should extend to protecting society from possible future crimes. But critics argue that judges don’t have badges and are supposed only to administer the law.

But that argument will not take center stage on Monday, and it is irrelevant, says Fox News senior legal analyst Judge Andrew Napolitano. He said the Supreme Court will deliberate over the Eight Amendment — not whether the judges were within their right to issue the sentences.

"It is a judge's role to police the Constitution, and determine whether or not the state government or the federal government is violating the Constitution," Napolitano said. "The federal Supreme Court doesn’t care if it's right or wrong — it just cares if the Eighth Amendment has been violated."

Bork and Napolitano said the Court will likely overturn the lower courts in a 5-4 decision — with the key vote coming from Justice Anthony Kennedy, who said in the 2005 Roper case that executing juveniles conflicted with “evolving standards of decency."

"It is less supportable to conclude that even a heinous crime committed by a juvenile is evidence of irretrievably depraved character," Kennedy wrote in 2005. "It would be misguided to equate the failings of a minor with those of an adult, for a greater possibility exists that a minor's character deficiencies will be reformed."

Fox News' Lee Ross and the Associated Press contributed to this report.