When it comes to combating terrorism, Pakistan is an indispensable ally for the United States. But as the two countries' checkered history shows, it is also an unreliable one. Two cases recently in the news demonstrate the duality of Pakistan's relationship with the United States: The arrest of Hafiz Mohammad Saeed, wanted by the United States but respected by many Pakistanis, and the imprisonment of Shakil Afridi, who helped pinpoint the location of Osama bin Laden....