It's absolutely critical, of course.
We went into Afghanistan at the beginning of 2002. We're still there in 2010. We'll be there for another year at a minimum. That mission has changed in many ways. The nature of the enemy's operations has changed. The nature of our equipment, our tactics, and our strategy has changed. The nature of the force that we are part of has changed. Anything that lasts ten years is bound to have that process of change.
But why are we there? I would argue it's still because our national interests are involved. They don't change. The tactics or perhaps the strategy may change, but the national interest I think stays the same. If our national interest is not served by participating in Afghanistan tomorrow, then in my view we should get out.