When spies don’t play well with their allies

Most C.I.A. veterans agree that no relationship between the spy agency and a foreign intelligence service is quite as byzantine, or as maddening, as that between the C.I.A. and Pakistan’s Directorate for Inter-Services Intelligence, or I.S.I. . . .

Without the I.S.I.’s help, American spies in Pakistan would be incapable of carrying out their primary mission in the country: hunting Islamic militants, including top members of Al Qaeda. Without the millions of covert American dollars sent annually to Pakistan, the I.S.I. would have trouble competing with the spy service of its archrival, India.

But the relationship is complicated by a web of competing interests. First off, the top American goal in the region is to shore up Afghanistan’s government and security services to better fight the I.S.I.’s traditional proxies, the Taliban, there.