In the conflict in Afghanistan, there are few stranger bedfellows than Iran and the Taliban. The former is the spiritual hub of Shiite Islam, while the latter is a vociferously anti-Shiite Sunni fundamentalist movement. Changing circumstances, however, have brought the onetime foes into a kind of partnership. Whatever its ideological differences with the insurgent outfit, Tehran has every reason to maintain its tactical partnership with the Taliban -- while also keeping its ties to the Afghan government....