Barack Obama has made a bold – even reckless – pledge. He has promised to shut the prison at Guantánamo Bay. But he does not have a clear plan for how to do it. He has admitted that it’s going to be hard. No question that it is the right thing to do. Guantánamo is the worst of the War on Terror: unjustifiable by the US’s own principles and laws, and, for those who think expediency is enough justification, not very successful at that. For most of its seven years, the 700 or so prisoners passing through have been small fry in terrorism – if they have had any discernible role at all – hardly living up to the drama of the barbed wire and world attention. But the nasty sequence of micro-decisions involved in emptying the camp of its 200 or so prisoners could chip away at the clarity of Obama’s bold declaration.

For the few prisoners who have been charged, or could be charged – no more than a few dozen – will he stick with the “military commissions” to try them? If he does, he contaminates himself with all the controversy that has surrounded these special courts. Their new rules were designed to cope, Bush officials said, with the difficulties of securing convictions against alleged terrorists picked up in the heat of battle.

Defence lawyers, including serving military officers appointed by the Pentagon, have said that they offer nothing like a fair trial and are simply intended to secure convictions in the absence of a case, even where the accused may have been bystanders scooped up by US soldiers or sold for bounty. Bush intended, with the Military Commissions Act 2006, to counter the criticism that the trials deprived prisoners of the normal rights to see evidence against them, and also allowed evidence gained from torture to be used. But defence lawyers say that normal rights to challenge evidence are still absent, and there is a continuing row, which the Bush team seems bent on spinning out to its last day, about whether waterboarding is torture (most of the world would say it is).

Obama needs to decide whether “tainted” evidence (his word for evidence extracted by these techniques) can be used, and whether he will use the commissions, or turn to regular US courts. The risk is that if he sticks to the pure line he could end up presiding over the release of the most important prisoners, against whom there seems to be a powerful, if “tainted” case. In particular, he must decide whether to accept the guilty plea of Khalid Sheikh Mohammed, the self-professed architect of 9/11, and one of the prisoners waterboarded by the CIA.

Where there is too little evidence to charge a prisoner, should Obama release him? Into the US, a country that (it’s worth betting on) the prisoner now loathes, whatever his feelings before capture? That is the politically unattractive conclusion. The risk for Obama is that one of these attacks Americans once free. Hence the scramble to persuade other countries to “rehome” them.

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