Leading article: Some light is thrown on a shadowy and malign force

Colin Powell may have vanished from the scene; not so Lawrence Wilkerson. The man who was chief of staff to the former Secretary of State has now become the most vocal critic of Iraq policy from within the US administration.

Last month, Mr Wilkerson accused the Vice-President Dick Cheney and Donald Rumsfeld, the Defence Secretary, of operating a cabal that ran the war, steamrollering General Powell and anyone else who dared to counsel restraint. This week, Mr Wilkerson elaborated. He told the Associated Press that President Bush was "too aloof, too distant in post-war planning" and this allowed Messrs Cheney and Rumsfeld to make policy on the treatment of prisoners that has returned to haunt the administration. In an interview with the BBC yesterday, he went further still, blaming Mr Cheney, the most powerful Vice-President in modern US history, for creating the climate that led to the abuse at Abu Ghraib and elsewhere, and implying that Mr Cheney might be liable to charges of war crimes.

Whether or not Mr Wilkerson is speaking for, or with the tacit blessing of, his former boss scarcely matters. Mr Powell had his chance to influence events. Instead, he was bested in bureaucratic combat by the Cheney/ Rumsfeld "cabal", while his reputation has been sullied - probably irreparably - by the now-infamous speech to the United Nations in which he made a bogus case for war, based on false evidence about Saddam Hussein's non-existent weapons. What matters is the light Mr Wilkerson throws on Mr Cheney's continuing malign influence on policy-making.

Mr Cheney has all along held two overriding beliefs. The first is in the supreme power of the presidency, a power that frees Mr Bush of the need to observe the constraints of international agreements. The second is that Islamic terrorism represents an existential threat to the United States. Therefore all means to defeat it are legitimate. From this mindset stem most of the decisions that have stained America's reputation: the reckless treatment of pre-war intelligence on weapons of mass destruction, ignoring the views of the UN and the International Atomic Energy Agency, the prison abuse scandals in Afghanistan, at Guantanamo Bay and Abu Ghraib - even the use of white phosphorus in Fallujah.

Perhaps the most poignant of Mr Wilkerson's claims this week was his recollection of General Powell once screaming down a phone to the Defence Secretary as the international furore grew about the US treatment of prisoners: "Donald, don't you understand what you are doing to our image?" Even if they understood, Donald and Dick evidently did not care.

In one sense, Mr Wilkerson's forays are part of a belated fightback by a defeated old guard with scores to settle. But they come as public opinion in America turns clearly against the war and questions the means employed to prosecute it. In recent weeks, the Senate has voted by overwhelming bipartisan margins to require the White House to give regular accounting of its policies, and to set explicit limits on interrogation techniques.

Amazingly, Mr Cheney is trying to reverse the latter vote. He is pleading for an exemption for the CIA, apparently not caring whether the rest of the world would thereby be convinced that the US government now sanctions torture. In the meantime, he defiantly insists that pre-war intelligence was properly used, accusing those who suggest otherwise of "reprehensible" attempts to "rewrite history". Some claim Mr Cheney has lost the President's favour, but there is scant sign of it. And until that happens, the world will see America less as a beacon of light than a harbinger of darkness.