One inspiration for such an initiative comes from Clarence Darrow, possibly the greatest defence lawyer that the US has ever known. He was an active Democrat in a Republican stronghold. In 1924 he defended two privileged young men, Richard Loeb and Nathan Leopold, who had killed Bobby Franks, a 14-year-old boy, as part of a cold-blooded plan to commit the perfect murder. The Leopold/Loeb murder outraged America, and the trial is among the most celebrated in American history. Darrow observed that "the court was the only thing standing between the boys and a bloodthirsty mob." And yet, he saved his clients from the gallows.

In a memorable summation, which convinced the judge to pass a sentence of life imprisonment rather than death by hanging, Darrow attacked the death penalty as atavistic, saying it "roots back to the beast and the jungle."

Time and time again, Darrow challenged the notion of "an eye for an eye": "If the state in which I live is not kinder, more humane, and more considerate than the mad act of these two boys, I am sorry I have lived so long." He went on to say: "I am pleading for the future; I am pleading for a time when hatred and cruelty will not control the hearts of men: when we can learn, by reason and judgment and understanding and faith, that all life is worth saving, and that mercy is the highest attribute of man."

This was American justice at its best. If Darrow were alive today, we can be sure he would have been at the forefront of challenging the Patriot Act, Guantànamo, Abu Ghraib, and extraordinary rendition. Yet, for all their deep problems, none of these controversial devices have yet yielded judicial death sentences.

Saddam's execution is on a different level altogether. If it goes ahead it will be the first time since the end of the cold war that a former head of state is executed as the result of a state-sanctioned judicial process: and executed, not by firing-squad, as is customary in Iraq for members of the officer corps, but hung as a common criminal.

Saddam was a bloodthirsty tyrant, and few could wish him freedom. However, according to almost all legal and human-rights experts, there was no fair trial. Before the trial began, the Iraqi government publicly declared Saddam guilty, and went on to remove judges who did not overtly support this belief, on one occasion precipitating the resignation of the entire defence team. Saddam's chief defence lawyer, Khamis al-Obaidi, a prominent Sunni public figure, was abducted, tortured and murdered by men claiming to be from the interior ministry.

Human Rights Watch has observed: "The government has not only interfered with the court's independence, but greatly undermined the court's own appearance of neutrality and objectivity. The transfer of the judge sends a chilling message to all judges: tow the line or risk removal." Can such a flawed process really be justification for the ultimate penalty?

Vengeance or justice?

Beyond that, westerners must take a hard look at what the consequences of Saddam's death might be. Are we sure that it will calm violence in Iraq and the region? Will it persuade anyone to put down their guns? Might it not, rather, harden the insurgency to take further retaliation against what might be seen as the ultimate symbol of the occupier's power, and the ultimate humiliation of smashed sovereignty?

Some are claiming that the Bush administration has influenced this trial at every stage, right up to and including the timing of the sentencing, in an effort to manipulate American public opinion to keep it in power. Whether or not this theory is true, it is widely believed. Democrats could now help Washington restore some of its lost legitimacy by joining the international call for clemency. If Americans were to unite behind such a call, it could have a transformative effect, not only within Iraq, but across the region.

The US intervention in Iraq has been presented by George W Bush and his principal ally Tony Blair as about values: offering the Iraqi people, and the entire middle east, the opportunity to embrace the values that underpin democratic civilisations. Those values, for the vast majority of democratic countries, including Britain and all other members of the European Union, include a firm and absolute rejection of the death penalty.

If America stands apart now, and allows Saddam to go to the gallows unchallenged, it sends a signal to the entire world that the US prefers to remain isolated from those who should be its closest allies and friends, and that the prevailing philosophy of its new "bipartisan" government is likely to continue as one of vengeance rather than justice and reconciliation.

If, however, America joins with its allies to petition for transmission of the sentence to one of life imprisonment, it would send the clearest possible signal to the world that a page in American history has been turned, and that an aberrant and damaging chapter may be drawing to a close.