Major territorial gains that began in provincial centers earlier this month came to a head on August 15, with the militant group waltzing into the national capital and seizing the city, encountering virtually no resistance from government forces in the process. With Afghan President Ashraf Ghani fleeing the country, the Taliban has installed a new president from its own ranks, insisting there would be no transitional state as it declared the "Islamic Emirate of Afghanistan" as the new government.  Having failed to prepare for the fall of the capital, Washington is now overseeing a hasty,...