And why did they do that? Because their target -- Ayman al-Zawahri, al Qaeda's second in command -- was in Pakistan, and the American effort might adversely affect Pakistan's President Pervez Musharraf.
A secret military operation in early 2005 to capture senior members of Al Qaeda in Pakistan’s tribal areas was aborted at the last minute after top Bush administration officials decided it was too risky and could jeopardize relations with Pakistan, according to intelligence and military officials.
The target was a meeting of Qaeda leaders that intelligence officials thought included Ayman al-Zawahri, Osama bin Laden’s top deputy and the man believed to run the terrorist group’s operations.
But the mission was called off after Donald H. Rumsfeld, then the defense secretary, rejected an 11th-hour appeal by Porter J. Goss, then the director of the Central Intelligence Agency, officials said. Members of a Navy Seals unit in parachute gear had already boarded C-130 cargo planes in Afghanistan when the mission was canceled, said a former senior intelligence official involved in the planning.
Mr. Rumsfeld decided that the operation, which had ballooned from a small number of military personnel and C.I.A. operatives to several hundred, was cumbersome and put too many American lives at risk, the current and former officials said. He was also concerned that it could cause a rift with Pakistan, an often reluctant ally that has barred the American military from operating in its tribal areas, the officials said.
The decision to halt the planned “snatch and grab” operation frustrated some top intelligence officials and members of the military’s secret Special Operations units, who say the United States missed a significant opportunity to try to capture senior members of Al Qaeda.
Their frustration has only grown over the past two years, they said, as Al Qaeda has improved its abilities to plan global attacks and build new training compounds in Pakistan’s tribal areas, which have become virtual havens for the terrorist network.
In recent months, the White House has become increasingly irritated with Pakistan’s president, Gen. Pervez Musharraf, for his inaction on the growing threat of the Taliban and Al Qaeda.
About a dozen current and former military and intelligence officials were interviewed for this article, all of whom requested anonymity because the planned 2005 mission remained classified.
Spokesmen for the Pentagon, the C.I.A. and the White House declined to comment. It is unclear whether President Bush was informed about the planned operation.
The officials acknowledge that they are not certain that Mr. Zawahri attended the 2005 meeting in North Waziristan, a mountainous province just miles from the Afghan border. But they said that the United States had communications intercepts that tipped them off to the meeting, and that intelligence officials had unusually high confidence that Mr. Zawahri was there.
Actually, in reading the whole story, the reason for calling off the attack seems, on the face of it, to be justifiable. The article states the number of troops involved grew to be several hundred, which makes it, as one source said, “... the invasion of Pakistan.”
The other is that failure would have been a total humiliation and possibly (probably?) destabilizing for Pakistan.
However, the story also notes that Pakistan has eased up in the fight against al Qaeda in the tribal areas western Pakistan that adjoin Afghanistan.
Here's a previous post that provides some useful background to that issue.