When Susan LeFevre was 19, she was arrested for selling drugs to an undercover officer in Saginaw, Mich. It was 1974, and she was a first-time offender. She believed that if she pleaded guilty, she would probably get probation.

She was wrong. After her guilty plea, she was sentenced to 10 to 20 years in state prison.

One year later, LeFevre hopped a fence and fled the prison. She moved to California and adopted her middle name, Marie. Years passed. She eventually married and raised three children, dedicating herself to her family and charitable causes. She never committed another offense. Her husband and children knew nothing about her youthful conviction or prison sentence — until April, when, 32 years after her escape, she was arrested and extradited to Michigan.

LeFevre's lawyers have asked the judge to set aside her drug sentence, but the local district attorney has filed new charges against her for escaping prison. If convicted, LeFevre could be sentenced to an additional five years on top of her drug sentence. It is almost certain that Michigan Gov. Jennifer Granholm will have to decide whether to commute LeFevre's sentence.

Supporters of clemency contend that locking up LeFevre would destroy her family and serve no purpose, as she already has done what the original sentencing judge urged her to do back in 1975: turn her life around. Opponents argue that commutation would send the wrong message and reward LeFevre's escape from prison. Both sides miss the bigger picture.

Sitting in her cell in Plymouth, Mich., LeFevre is one of 2 million Americans behind bars. Many of them, like LeFevre, are nonviolent drug offenders. The staggering number of American prisoners has made the United States the world's leading incarcerator; this nation locks up a greater number of offenders for longer periods than any other nation. In 1960, approximately 330,000 people were behind bars in the United States. Today, the number is 2.3 million. Moreover, largely because of the "war on drugs," the increase in women's incarceration in recent years has far outstripped the increase in men's, devastating many families and communities.

How did we scale the soaring peaks of mass incarceration? The decline of mercy has played a leading role. With the noble intent of bringing rationality and order to what had often been a chaotic and even discriminatory system of criminal justice, reformers at every stage of the justice system have sought to limit the power of discretionary actors to say no to punitive policies.

Consider: Police departments have instituted mandatory arrest and "zero tolerance" policies that have swept up many low-level offenders. Prosecutors' offices have given instructions, such as those issued by a series of Republican attorneys general, to charge only the most serious provable offenses, no matter what the circumstances. Juries have convicted defendants on charges without any inkling of the sentencing consequences. The ability of sentencing judges to respond to cases on their individual merits has been sharply curtailed or destroyed by sentencing guidelines and mandatory minimum sentences. And the granting of executive clemency has radically declined, not just in the Bush administration but also in governors' offices.

One might think that the courts and the Constitution provide a safeguard against excessive punishment; after all, the Eighth Amendment promises protection against "cruel and unusual punishments." But the Supreme Court has interpreted this provision to require great deference to state legislatures. The court, for example, has upheld sentences of 25 years to life and 50 years to life — imposed under California's "three strikes" law — for repeat offenders who, respectively, stole three golf clubs from a pro shop and shoplifted nine videotapes from a Kmart.

An exit strategy from this upward spiral of incarceration lies in revitalizing the exercise of mercy. Yes, mercy carries the risk of arbitrariness and discrimination. Soccer moms such as Marie LeFevre may seem to be more appealing defendants than many others who have committed nonviolent crimes. But mass incarceration has had an enormous impact on poor and minority communities. Only by reconsidering individual cases and questioning the necessity and desirability of punishment can we turn back from the prison state that we have become.

Our Founding Fathers understood the importance of checks and balances, but no one is checking or balancing the decisions that are causing our prisons to overflow. By reinvigorating the veto power of actors all along the justice system, we may save individuals from unnecessarily destroyed lives. We may save money in these economically trying times. But most important, we may save ourselves — by preserving the value of mercy.

Carol S. Steiker is a professor at Harvard Law School. She wrote this commentary for The Washington Post.