Last month driving up Afghanistan's magnificent Panjshir valley, you couldn't help thinking if the resurgent Taliban would ever be able to break its defences, both natural and from the Tajik-dominated populace. With its jagged cliffs and plunging valleys, Panjshir has been largely out of bounds  for the  Taliban, whether during the civil war or in the past 10 years when it has expanded a deadly insurgency against western and Afghan forces across the country. But on Saturday, the insurgents struck, carrying out a suicide bombing at a provincial reconstruction team base housing U.S. and Afghan troops and officials.