The latest revelation about George W Bush's involvement in the Valerie Plame scandal is unlikely to be the smoking gun that finishes off his administration, writes David Fickling.
But it is the most damaging allegation yet to emerge about Bush's involvement in the campaign to discredit a high-ranking critic of his Iraq policy.
So far, Bush has been more or less insulated from the Plame scandal. Despite nearly three years of inquiries and investigations into the affair, the buck has always stopped at the door of Washington's political advisers, rather than their masters.
Now there is the suggestion that Bush and Cheney may have respectively given their subordinates permission and encouragement in the campaign against Valerie Plame's husband, Joseph Wilson.
According to court testimony from Cheney's chief of staff Lewis "Scooter" Libby, Libby was told by Cheney that Bush had given his permission to leak parts of the classified National Intelligence Estimate. This classified information could be read as contradicting Wilson's criticisms.
The documents claim that Cheney wanted it put about that Wilson had only got a "junket" to investigate claims that Iraq had tried to buy uranium from Niger because of the intervention of his wife Plame, a CIA operative. The intention was to undermine Wilson's credibility by arguing that his fact-finding mission was little more than "an assignment on account of nepotism".
What makes all this particularly damaging is that Bush has spent almost three years denying that he knew anything about leaks from the White House.
In 2003, soon after the scandal broke, he told reporters: "I don't know of anybody in my administration who leaked classified information. If somebody did leak classified information, I'd like to know it and we'll take the appropriate action."
If it is found out that Bush did authorise the leak - and at the moment the only evidence we have of this is third-hand, via Libby and Cheney, and in testimony by Libby over which he is on trial for perjury - those denials would be exposed as stone-cold lies.
There is a technicality Bush could use to get out of all this. Since the president is allowed to declassify whatever secret information he wants, he would be able to argue that he has not "leaked" any information at all, only declassified it in a somewhat unconventional way. A senior administration official tells today's Washington Post, that Bush "sees a distinction between leaks and what he is alleged to have done".
Whether such sophistry, with its easily satirised echoes of Yes, Prime Minister, would wash with an American public already losing faith in their president and his conduct of the war is another question.
The more likely escape clause is simply the complexity and confusion of the case. Wikipedia's entry on the Plame case already runs to more than 20,000 words.
