Four months after the 9/11 commission’s report on intelligence failures leading up to the terrorist attacks of Sept. 11, a shakeup at the Central Intelligence Agency is underway. Resignations are piling up throughout the intelligence community—but not at the Federal Bureau of Investigation, which had its own counterterrorism mishaps before Sept. 11, according to the commission report. The C.I.A. dismantles threats overseas; the F.B.I. works inside the U.S. That rough division of labor places the responsibility for keeping the 19 hijackers from boarding planes on Sept. 11 squarely in the F.B.I.’s hands.