There is a risk that leaving too few troops after 2014 would stop or stall the already slow development of the Afghan army and police, whose competence -- and that of the Afghan government as a whole -- is crucial to ending the war successfully.
On the other hand, keeping too many foreign troops beyond 2014 might only prolong Afghanistan's dependence upon them, while Western forces absorb even more casualties. Perhaps the greatest risk is that a wrong calculation by the U.S. on troop levels could enable the Taliban and affiliated insurgents to regain lost territory and influence.
President Barack Obama has pledged to wind down the 11-year-old war, even as Congress presses for an accelerated withdrawal. The intent, approved by NATO in 2010, is to remove combat forces by the end of 2014 but to continue yet-to-be-defined security assistance.
Defense Secretary Leon Panetta has described the broad outlines of a post-2014 plan that amounts to a scaled-down version of what U.S. and NATO forces are already doing: fighting terrorists, training and assisting the Afghan forces, and providing logistical support.
