Before the Sept. 11 attacks, the N.S.A. normally eavesdropped on a small number of American citizens or resident aliens, often a dozen or less, while the F.B.I., whose low-tech wiretapping was far less intrusive, requested most of the warrants from FISA.
Despite the low odds of having a request turned down, President Bush established a secret program in which the N.S.A. would bypass the FISA court and begin eavesdropping without warrant on Americans. This decision seems to have been based on a new concept of monitoring by the agency, a way, according to the administration, to effectively handle all the data and new information.
At the time, the buzzword in national security circles was data mining: digging deep into piles of information to come up with some pattern or clue to what might happen next. Rather than monitoring a dozen or so people for months at a time, as had been the practice, the decision was made to begin secretly eavesdropping on hundreds, perhaps thousands, of people for just a few days or a week at a time in order to determine who posed potential threats.
Those deemed innocent would quickly be eliminated from the watch list, while those thought suspicious would be submitted to the FISA court for a warrant.
In essence, N.S.A. seemed to be on a classic fishing expedition, precisely the type of abuse the FISA court was put in place to stop.At a news conference, President Bush himself seemed to acknowledge this new tactic. "FISA is for long-term monitoring," he said. "There's a difference between detecting so we can prevent, and monitoring.