The stunningly light sentence handed to Osama bin Laden's former driver will dismay the White House, as the trial of Salim Hamdan was something of a showcase hearing, the very first war crimes trial at Guantanamo Bay seven years after the September 11 attacks.

After seeking 30 years in prison for Hamdan, in a military tribunal, before a military jury, and in a trial where many rights normally afforded defendants in a civilian court were greatly curtailed, the five and a half year sentence was nothing short of a disaster for the Bush administration.

It now finds itself in the unattractive position - in the eyes of civil libertarians and much of the international community at least - of refusing to release Hamdan even after he completes his sentence. He is eligible for release in just five months, but the White House has made clear for months that whatever happened to Hamdan, he would still be held indefinitely because of his classification as an "unlawful enemy combatant".

The six-member jury of military officers had already made clear that they were not there to do the prosecution's bidding when they acquitted Hamdan on Wednesday of the more serious charge of conspiring to attack civilians, finding him guilty instead on the lesser charge of providing support to al-Qaeda. He was arrested at a road block in Afghanistan in November 2001, with two surface-to-air missiles in his car.

The reality in the US is that the fate of Hamdan, and that of the Guantanamo facility itself, lies in the hands of Mr Bush's successor, when he takes office in January.

Barack Obama and John McCain have both pledged to close Guantanamo, although Mr McCain supported the legislation that made the tribunal system at the US Naval Base possible. It was declared unconstitutional by the US Supreme Court in 2006, but reconstituted, with modifications, by Congress.

Yet what to do with Hamdan is a far from straightforward decision for the next president. If he enters the Oval Office Mr Obama, in particular, will come under significant pressure to release him, by rights groups at home and perhaps even more so by allies abroad, to whom he has pledged a new style of US governance rooted in the ideals of open justice and human dignity.

But as he seeks the White House against his Republican opponent John McCain, Mr Obama has already begun to sound a more centrist, and at times hawkish note, when it comes to America's enemies. It would be politically untenable for him to release Hamdan and allow bin Laden's former driver to roam the streets of America a free man, in a country where the September 11 attacks, although fading as the primary election issue, remain a seminal event burnt into the American psyche.

Sending Hamdan back to his native Yemen, if he was to be released, would appear to be the only option, yet there would be no guarantee of his safety there by a government whose human rights record is poor and which is striving to combat the forces of Islamic militancy inside its own borders.

Closing down Guantanamo is also a political and logistical minefield. There are still over 200 prisoners there, many of whom are considered genuinely dangerous. Faced with the reality of closing the facility down, many US voters will chafe at the idea.

The other problem is what to do with the inmates if Guantanamo is closed. After a recent Supreme Court ruling, the detainess now have the right to challenge their indefinite detention in US federal court. Dozens of hearings are likely in coming years in which detainees, now properly represented by civilian lawyers, petition federal courts to challenge their detention as enemy combatants held without charge. It is a legal mess that will likely leave Guantanamo operating for a considerable time.

Only a handful of the inmates have actually been charged under the military commission system, with Hamdan being one of them. The Bush administration has been accused of expediting Hamdan's hearing so that they could get the tribunal system under way to force Mr Bush's successor to maintain it. Last night's verdict was the last thing they wanted - or expected.

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