Insurgent leaders, they say, have redoubled a campaign to assassinate key Afghan government and security officials who are likely to play leadership roles in the country once foreign troops depart. And by happenstance or meticulous planning — U.S. military officials are not sure which — the Taliban has managed to kill numerous Western troops by joining the ranks of the Afghan army.

“The Taliban are fighting a political war while the United States and its allies are still fighting a tactical military war,” said Joshua Foust, a former U.S. intelligence analyst who has worked in Afghanistan and is now a fellow with the American Security Project. “We remain focused on terrain. They are focused on attacking the transition process and seizing the narrative of victory.”

The impact of the strategic shift, which has occurred gradually over the past year, has been profound. The high-profile assaults and assassinations have prompted new doubts among Afghans about the ability of their government and security forces to keep the insurgents at bay once NATO’s combat mission ends in 2014.