[##_1L|1396992692.jpg|width="131" height="91" alt=""|_##]Advocates of greater fairness in criminal sentencing won an important battle at the U.S. Supreme Court last week. But they could lose the war if individual judges exploit the decision to return to the bad old days of dramatically divergent sentences for the same crime. By a 7-2 vote in two drug cases, the justices -- reversing federal appeals courts -- upheld sentences imposed by federal district judges that were more lenient than those suggested by guidelines of the U.S. Sentencing Commission. In one case, Brian Gall, who was involved in an Ecstasy ring in college but reformed himself, was sentenced to probation. In the other, Derrick Kimbrough, a veteran of the Persian Gulf War who pleaded guilty to possessing crack and powder cocaine, received a 15-year sentence instead of the 19 to 22 years he would have gotten under the guidelines.

Kimbrough's case had attracted particular attention because it involved a disparity in sentencing for crack and powder cocaine that disproportionately punishes African Americans. The judge in Kimbrough's case rightly had described the 100-1 disparity -- which the commission adopted to reflect a similar formula in an act of Congress -- as "ridiculous."

Coincidentally, the Sentencing Commission, which already had voted to narrow the disparity, decided last week to make the reduction retroactive. That could allow nearly 20,000 inmates to petition for sentence reductions. It will not, however, undo the crack/powder differential contained in a draconian 1986 law establishing mandatory minimum terms for drug offenses. Only Congress can, and should, repeal those provisions.

Still, the court's rulings reflect the national reconsideration of the misguided crack/powder distinction. Unfortunately, they could lead to other sorts of unfairness. To understand why, it is worth recalling why Congress created the Sentencing Commission in 1984. Faced with evidence of wildly different sentences being imposed for the same crime -- some of which seemed to track racial differences -- Congress decided the commission should devise sentences that would reflect several factors: the seriousness of the offense, the defendant's criminal history, and aggravating and mitigating factors. Although the rules adopted by the commission (subject to congressional veto) were called "guidelines," they were for practical purposes mandatory.

Fast forward to 2005, when the Supreme Court ruled 5 to 4 that the 6th Amendment required juries, not judges, to weigh aggravating factors that could increase a convicted defendant's sentence. Therefore, it was unconstitutional to require judges to abide by guidelines based on such factors. But a different 5-4 majority said the commission's guidelines could remain on the books as an "advisory" resource for judges.

In June of this year, the court seemed to shore up the guidelines when it ruled that an appeals court was free to presume that sentences within the guidelines were reasonable. But last week, the pendulum swung back in the direction of greater leeway for the sentencing judge. Although judges must treat the guidelines as a starting point, Justice John Paul Stevens wrote in the Gall case, their greater familiarity with the case entitles them to deference when they sentence outside the guidelines.

Once again, the high court has left lawyers and lower-court judges scratching their heads over how much discretion in sentencing is too much. At least some judges will see the latest rulings as a green light for departures from the guidelines much less defensible than the one in the Kimbrough case. Racial, and regional, differences in sentencing may reassert themselves. A judge might even feel free to act on a personal view that crack cocaine is more dangerous than powder.

No matter how criminal sentences are determined, two traditional notions of justice are in tension with one another. One is that similar crimes (and criminals) should be punished similarly. The other is that justice consists of taking account of the circumstances of a particular case. The sentencing guidelines on which the court cast doubt last week didn't resolve that tension perfectly, but they were an improvement over the pre-guidelines era that mocked the concept of "equal justice under law."