It has long been argued that the United States had the opportunity to kill or capture Osama bin Laden and deal a decisive blow to al Qaeda at Tora Bora, a battle in the mountainous terrain along the eastern border of Afghanistan.  Why it didn't is a story in itself.   

The Taliban were defeated in a few months primarily by troops of the "Northern Alliance"  and supportive efforts of U.S. and NATO air forces.  U.S. and NATO ground forces were also involved as were operational agents of the U.S. Central Intelligence Agency.  Hamid Karzai is currently the president of Afghanistan.

To further summarize what has occurred:

In the fight for Tora Bora, corrupt local militias did not live up to promises to seal off the mountain redoubt, and some colluded in the escape of fleeing al Qaeda fighters. Franks did not perceive the setbacks soon enough, some officials said, because he ran the war from Tampa with no commander on the scene above the rank of lieutenant colonel. The first Americans did not arrive until three days into the fighting. "No one had the big picture," one defense official said.  The Bush administration has never acknowledged that bin Laden slipped through the cordon ostensibly placed around Tora Bora as U.S. aircraft began bombing on Nov. 30. Until now it was not known publicly whether the al Qaeda leader was present on the battlefield.  But inside the government there is little controversy on the subject. Captured al Qaeda fighters, interviewed separately, gave consistent accounts describing an address by bin Laden around Dec. 3 to mujaheddin, or holy warriors, dug into the warren of caves and tunnels built as a redoubt against Soviet invaders in the 1980s. One official said "we had a good piece of sigint," or signals intelligence, confirming those reports.  "I don't think you can ever say with certainty, but we did conclude he was there, and that conclusion has strengthened with time," said another official, giving an authoritative account of the intelligence consensus. "We have high confidence that he was there, and also high confidence, but not as high, that he got out.

It isn’t exactly true that U.S. forces weren't provided the opportunity to deal a blow to Al Qaeda and even find bin Laden:

The best chance at killing or capture (of bin Laden) may have been deep in the past. Below the white peaks of the Spin Ghar near the Pakistani line, Osama bin Laden was spotted, in late November and early December 2001, along with at least 1,000 of his Qaeda fighters. The American high command believed this was it but didn't want to put its soldiers -- even Delta Force, renowned for risk-taking -- in severe danger; didn't want British special forces -- who also had teams in the area, eager to move in -- to claim the war's greatest prize; and couldn't compel Pakistan to close off the frontier. (Why the Americans didn't block the frontier themselves has never become clear, though the perils of landing helicopters at high altitudes in terrible weather probably played a part.) Without much support on the ground, with only the troops of Afghan warlords to rely on, a bombardment from American jets merely chased bin Laden between the ridges, most think, and across the border. 

"Across the border" means into the Tribal Areas of Pakistan.

While what is stated above is still true, significant changes in U.S. policy brought about by a new administration as well as events in Afghanistan and Pakistan, make this an opportune time to look again at Central Asia, the Taliban and Al Qaeda. Before proceeding, the following needs to be understood.

1.  The U.S. and NATO are conducting military operations against the Taliban in Afghanistan.

2.  Current intelligence indicates that the strongest elements of Al Qaeda are located in Pakistan's Tribal Areas. 

3.  The Taliban and Al Qaeda are mutually supportive.

4. Facing impeachment, Pervez Musharraf resigned as president of Pakistan.

5.  Pakistani Prime Minister Benazir Bhutto was likely to win the 2008 General  Election in Pakistan and become president but was assassinated two weeks before the election.

6.  Asif Ali Zardari is now the president of Pakistan.

7.  Pakistan is a nuclear weapons state.

At this time, the National Security of the United States, Afghanistan and Pakistan seem inexorably linked. The circumstances in Central Asia are critical.  The Taliban are waging war in both Afghanistan and Pakistan.  The Pakistani army is severely challenged in the Tribal Areas, an area the Taliban have infested.  U.S. President Barack Obama has set a high priority on stabilizing both governments.  With the concurrence of Secretary of Defense Robert Gates and General David Petraous, the head of U.S. Central Command, President Obama has deployed additional troops to Afghanistan; 17,000 U.S. are slated for a combat role, another 4,000 as advisers.   He is also asking Congress for 17 billion USD to assist the government in Pakistan.  The purported mission scope is to strengthen the governments in both countries so they can deal with the challenges they face themselves. Changes in U.S. strategy are also apparent.  Top American commander in Afghanistan, General David McKiernan has been replaces by Lt. General Stanley McChrystal, whose expertise in special operations proved valuable in turning around what was perceived as a rapidly deteriorating situation in Iraq in 2006. Emphasis will be on protecting the civilian population as well as dealing with threats to the established government, a focus that seemed to work in Iraq.

McChrystal did make one mistake.  While in charge of special operations in Afghanistan, he reported the death of Army Ranger and former NFL star with the Arizona Cardinals Pat Tillman resulted from enemy hostilities.  A Pentagon investigation concluded that Tillman was killed from "friendly fire."  McChrystal's new job is not likely to be an easy one. The situation in Pakistan is even more ominous.  After the brutal changes in government, the new president is struggling with the Pakistani military in dealing with Taliban incursions into the Tribal Areas.  Moreover Pakistan is a nuclear weapons state.

Members of Congress have been told in confidential briefings that Pakistan is rapidly adding to its nuclear arsenal even while racked by insurgency, raising questions on Capitol Hill about whether billions of dollars in proposed military aid might be diverted to Pakistan’s nuclear program. Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, confirmed the assessment of the expanded arsenal in a one-word answer to a question on Thursday in the midst of lengthy Senate testimony. Sitting beside Defense Secretary Robert M. Gates, he was asked whether he had seen evidence of an increase in the size of the Pakistani nuclear arsenal. “Yes,” he said quickly, adding nothing, clearly cognizant of Pakistan’s sensitivity to any discussion about the country’s nuclear strategy or security.

It is already known that the United States has taken steps to help keep Pakistani nuclear weapons secure.  The Taliban insurgency has been as close as 150 km to one of Pakistan's nuclear stockpiles. However a military response alone will not be adequate. The U.S. effort is also going to have an increased diplomatic component.  Asking greater commitment from European NATO allies will certainly become one looming facet. Secretary of State Hillary Clinton has held meetings with the presidents of both Afghanistan and Pakistan, realizing that U.S. National Security is so closely tied to what happens in those two countries.  

And so it is a great privilege to welcome President Karzai and President Zardari. I have known President Zardari for a longer period of time, going back many years now. And I was a great admirer and a friend of his late wife, who I thought was an extraordinary leader. And I am pleased to welcome him here as the democratically elected president of his country.  We have made this common cause because we face a common threat, and we have a common task and a common challenge. We know that each of your countries is struggling with the extremists who would destabilize and undermine democracy. An ancient Afghan proverb says “Patience is bitter, but its fruit is sweet.” We know that this consultation is part of a continuing process. It began with our first trilateral. It continued with the international conference in The Hague, with the Tokyo donors conference, and now we are once again meeting here in Washington. 

Sounds good, however:

As the Obama administration expands U.S. involvement in Afghanistan, military experts are warning that the United States is taking on security and political commitments that will last at least a decade and a cost that will probably eclipse that of the Iraq war.

There is a lot at stake for the nations involved.  President Obama is trying to initiate new ideas instead of prolonging the policy failures of the past but as yet it hasn't been clearly stated or estimated what the costs of dealing with unfavorable conditions that now exist will be.   We should not go down this road again.