On March 27, President Obama announced a new strategy for Afghanistan and Pakistan. This, in part, is what he said:

Many people in the United States--and many in partner countries that have sacrificed so much--have a simple question: What is our purpose in Afghanistan? After so many years, they ask, why do our men and women still fight and die there? And they deserve a straightforward answer.

So let me be clear: Al Qaeda and its allies--the terrorist who planned and supported the 9/11 attacks--are in Pakistan and Afghanistan. Multiple intelligence estimates have warned that al Qaeda is actively planning attacks on the United States homeland from its safe haven in Pakistan. And if the Afghan government falls to the Taliban – or allows al Qaeda to go unchallenged--that country will again be a base for terrorists who want to kill as many of our people as they possibly can.

The future of Afghanistan is inextricably linked to the future of its neighbor, Pakistan. In the nearly eight years since 9/11, al Qaeda and its extremist allies have moved across the border to the remote areas of the Pakistani frontier. … For the American people, this border region has become the most dangerous place in the world.

As President, my greatest responsibility is to protect the American people. We are not in Afghanistan to control that country or to dictate its future. We are in Afghanistan to confront a common enemy that threatens the United States, our friends and our allies, and the people of Afghanistan and Pakistan to have suffered the most at the hand of violent extremists.

So I want the American people to understand that we have a clear and focused goal: to disrupt, dismantle and defeat al Qaeda in Pakistan and Afghanistan, and to prevent their return to either country in the future. That’s the goal that must be achieved. That is a cause that could not be more just. And to the terrorists who oppose us, my message is the same: We will defeat you.

President Obama could not have been clearer in articulating his understanding of the fundamental national interests at stake in Afghanistan. And nothing that has happened in the past six months affects--or should affect--that understanding. That includes the controversy over the Afghan elections. If what the president said was true in March, it remains true today.

Two things have changed, however. First, the American people have become increasingly impatient with our involvement in Afghanistan, and Democrats have turned against it. And second, the commander of our forces in Afghanistan has concluded that without substantial additional resources--including troops--he cannot hope to achieve the objectives the president has articulated. As General McChrystal put it in his August 30 assessment,

Our campaign in Afghanistan has been historically under-resourced and remains so today. Almost every aspect of our collective effort and associated resourcing have lagged a growing insurgency--historically a recipe for failure in COIN [counter insurgency]. Success will require a discrete “jump” to gain the initiative, demonstrate progress in the short term, and secure long-term support. Resources will not win this war, but under-resourcing could lose it. … Ideally, the ANSF [Afghan National Security Force] must lead this fight, but they will not have enough capability in the near-term given the insurgency’s growth rate. In the interim, coalition forces must provide a bridge capability to protect critical segments of the population. The status quo will lead to failure if we wait for the ANSF to grow.

President Obama now faces a fateful choice. Either he must authorize the troops needed to achieve the mission he defined six months ago, or he must redefine the mission to comport with the level of deployments he decides the American people will accept. One thing is clear: If the president accurately characterized the stakes in March, then reducing our mission in Afghanistan means increasing the risks to the American people. If he chooses that course, he owes it to the country to describe the risks as bluntly as he previously described the stakes.