The FBI is the only game in town for counterterrorism. The CIA & the rest of the spook alphabet soup are headed by military or ex-military, their budgets are controlled by the Pentagon, & all their emphasis is now on supporting the war-fighter. Ironic, because the CIA was set up as a counterbalance to the military's intel outfits, but OSS & CIA were never v. effective - see Vietnam, Korean War, PRC, nuclear secrets, Bay of Pigs, fall of the Shah of Iran, & on & on. Dept. State & their intel agency are now just a sideshow in our foreign policy bigtop, with regional military comanders-in-chief, their own intel, & military aid largess to spread around.
CIA BY LAW can not operate inside the US, they had nothing to do with this debacle.
(My bold)
Agreed, in theory. & FBI under Hoover was not supposed to be wiretapping, running black bag ops, intercepting mail, collecting personal info for political blackmail, & on & on. Yah, CIA is/was supposed to hand-off to FBI when foreign targets cross borders into the US, & picked up again when they left. We know how well that worked up until 09/11, & FBI is still working on getting into the electronic age.
FBI is improving, but it still needs more time. The worry is that the clock is ticking, & the time to the next mass outrage - I don't count the Boston Marathon, they seemed to be more about causing injuries than mass deaths (no disrespect to the dead & wounded nor their families; their suffering is too real) - is coming due.