By Kevin Connolly
BBC News, Washington
Details of the CIA's secret programme are beginning to emerge
In the world of intelligence gathering the past never really goes away - it stays around to haunt the present and set traps for the future.
The issue of how America conducted its "war on terror" - who it tortured and detained and on whose orders - is full of such traps.
We know that Barack Obama knows this - he talks about the need to move forward rather than to look back - but that is no guarantee that he will be able to resist calls for some sort of investigation of the Bush administration's intelligence policies.
The argument from the human rights lobby and the left of the Democratic Party appears to have gained ground in Washington in the last week or so - some sort of enquiry is now necessary, they believe, to re-assert the rule of law and restore America to the moral high ground of international diplomacy.
The case against re-opening the wounds of the recent past lacks moral clarity, perhaps, but it is no less passionately held among Republicans.
Washing too much dirty linen in public too quickly, they point out, might compromise ongoing counter-terrorism operations, embarrass some of America's loyal allies and even risk alienating some intelligence professionals who carried out orders under President George W Bush and who continue to do so under Barack Obama.
Alleged atrocity occurred as Gen Dostum took charge of some 4,000 prisoners amid a mass Taliban surrender in late November 2001
Prisoners were being transported from Kunduz to Sheberghan prison, west of Mazar-e-Sharif
Allegations of massacre heard by two investigators from Physicians for Human Rights, who visited prison at Sheberghan in January 2002; investigators later uncovered apparent mass grave at Dasht-e Leili
Newsweek reports deaths occurred from suffocation among prisoners packed one on top of another in the containers; testimony gathered by New York Times suggests prisoners were also fired on and killed while inside containers
Alleged survivors told Newsweek they were so desperate with thirst that they licked perspiration from each other's bodies
You could perhaps mount an enquiry into a single incident - like the allegation that America's ally General Abdul Rashid Dostum may have murdered Taliban prisoners in 2001 - without creating too much domestic political fallout.
But anything more broad-ranging would carry considerable political risk.
Stories about intelligence issues in all media outlets - and this one is no exception - are frequently confused and confusing.
That is natural enough - very often such facts as we know have been put into the public domain by intelligence officials with axes to grind and there is no way to verify them.
So it makes sense to start with the politics of what is going on in Washington - at least there the motives of all concerned are easy enough to unpick.
So, for example, there are Democrats, led by Senator Patrick Leahy, chair of the Senate Judiciary Committee, who would like to see a commission of enquiry into allegations of CIA involvement in the torture of terrorism suspects.
Any sort of enquiry will suck the air out of Washington politics and make it very difficult for Mr Obama to continue his search for the elusive spirit of bi-partisanship on tricky issues like healthcare reform
At the same time, Attorney-General Eric Holder has let it be known that he is considering appointing a special prosecutor to look into those allegations, too.
You could take the Machiavellian view that Mr Holder has been put forward by the administration to make it look as though it is considering re-opening this huge seething can of worms and that in the end the White House will quietly shelve the whole affair.
But either way, it has to be acknowledged at the moment that the push from the left for something to be done is huge.
Forces of darkness
The White House, of course, is alive to the obvious political danger.
First, any sort of enquiry will suck the air out of Washington politics and make it very difficult for Mr Obama to continue his search for the elusive spirit of bi-partisanship on tricky issues like healthcare reform.
And second, in a country where power tends to alternate between parties of the right and left, one sure way to guarantee inquiries into Democratic administrations of the future is to stage one into a Republican administration of the past.
But some Democrats will not be deterred by that kind of pragmatism.
There is a strong view in some quarters on the left that in its reaction to the terror attacks on 9/11, the Bush administration strayed far outside the law and the constitution it should have been upholding.
In this version of the recent past, the former Vice-President Dick Cheney is portrayed as a figure of grim malevolence, conjuring and orchestrating the forces of darkness behind the throne.
Are Dick Cheney's actions coming back to haunt Mr Obama?
Part of the Democrats' motivation is to hold Mr Cheney accountable for his actions - or in plain English, to "get him".
So, not surprisingly, Mr Cheney is also a central figure in the other strand of an increasingly complex web of allegations - this time about the relationship between Congress and the CIA.
The charge against Mr Cheney is that he instructed senior CIA officers to conceal from Congress the existence of a secret operation, set up after 9/11.
American law does arguably provide for such concealment - although only temporarily and in the most exceptional circumstances.
Essentially, though, the intelligence agencies are fully accountable to Congress and any deviation from that accountability would be hugely sensitive.
Democrats say they only found out about the operation when its existence was disclosed last month to the new director of the CIA, Leon Panetta, who immediately closed it down and came to Capitol Hill to brief them.
They say this is important mainly because the CIA's accountability to Congress appears to have been compromised.
One possible solution being mooted is to increase from eight to 40 or 50 the number of senior members of the House who are routinely briefed on such matters.
That is another suggestion towards which the White House is lukewarm at best.
Republicans sense this may all be some kind of smokescreen to protect the Democratic Speaker of the House Nancy Pelosi, who has yet to provide a full explanation of her own claim that the CIA directly lied to her about the use of waterboarding in the early years of the "war on terror".
That claim had the effect of deflecting claims that Speaker Pelosi had known all about the practice of waterboarding which she later said she deplored.
From the Democrats' point of view, making the issue a general one about the relationship between Congress and the CIA tends to deflect attention from Speaker Pelosi.
The linking thread in these various issues?
Well, that is the whole question of the extent to which - if at all - the energies of the Obama years should be spent staging investigations - and perhaps prosecutions - based on American actions during the administration of George W Bush.
For Mr Obama, this is an acute, and increasingly pressing dilemma.
He has to weigh the need to remain true to his grassroots supporters (and perhaps his own instincts) against the dangers of alienating the intelligence establishment and poisoning the political atmosphere in Washington.
We know him on such issues to be cautious and pragmatic - his decision on this delicate issue will tell us a good deal more about his political judgement.