As fresh details of the US/Saudi intelligence coup over the foiled al-Qa'ida bomb plot emerged yesterday, senior Democrats and Republicans called for a full investigation into how the news became public, amid fears that the leak could jeopardise other operations.
Every sign is that the sting was, as one Obama administration official put it, "a 1-2 blow against al-Qa'ida in the Arabian Peninsula (AQAP)". The Saudi agent who infiltrated the Yemen-based group, posing as a would-be suicide bomber, not only managed to secure the sophisticated device that was to have been exploded aboard a US-bound commercial flight, and pass it to the Saudis and their CIA partners.
He also provided information that led to the drone attack which killed Fahd Mohammed al-Quso, a top operative of AQAP's Yemen branch, at the weekend. Al-Quso is believed to have been behind the suicide attack on the destroyer USS Cole at Aden in 2000.
The agent is believed to have been moved with his relatives to a secure location after word emerged of how the plot was disrupted, and that the person supposed to carry it out was working for Saudi intelligence and the CIA.
The device, believed to be the work of a master bomb-maker, Ibrahim Hassan al-Asiri, is still being examined by the FBI but already appears to be Mr Asiri's most lethal offering yet. Sewn into "custom-fit" underwear, it is said to have a double detonator and to contain no metal, making it especially hard for airport security to detect. The high-grade military explosive inside "undoubtedly would have brought down an aircraft", officials told The New York Times.
But although the CIA operation has yielded rich dividends, it has also served notice that AQAP remains a major threat to the US, despite a series of damaging setbacks and the loss of several key operatives to drone strikes. That continuing threat has sparked anger on Capitol Hill and in US intelligence and counterterrorism agencies at how word of the foiled bomb plot was leaked. The Associated Press news agency learnt of it last week, but agreed to not to publish. It finally did so on Monday, only after Sunday's attack on al-Quso and, presumably, once the safety of the Saudi mole was assured.
"This leak could have been devastating and could still do significant long term damage," said Peter King, the Republican chairman of the House Homeland Security Committee. He added that even a hint of it had emerged was "really, really shocking".
Unusually, congressional indignation is not partisan. Charles Ruppersberger, the top Democrat on Mr King's panel, backed calls for an inquiry, saying: "When you have a leak it could cost American lives, your allies' lives."
The thwarting of the plot is a sign of better co-operation between the US and Saudi security services. After the 9/11 attacks carried out by 19 hijackers – of whom 15 were Saudis – there were complaints in Washington that Riyadh was dragging its heels in the struggle against al-Qa'ida. Now tribal and family links between Saudi Arabia and Yemen are proving an Achilles' heel for the organisation.