So what happened next? I don't know whether this is surprising or not, but Richard Schmitt of the LA Times reports today that after the spike in 2002, those two trends diverged. There have been more and more surveillance warrants issued, but they've produced fewer and fewer actual prosecutions:
The emphasis on spy programs  is starting to give pause to some members of Congress who fear the government is investing too much in anti-terrorism programs at the expense of traditional crime-fighting. Other lawmakers are raising questions about how well the FBI is performing its counter-terrorism mission.If anything, the real situation is almost certainly even worse than this: "Warrants" understates the vast increase in surveillance, which also includes things like national security letters and the warrantless programs run by the NSA, while "prosecutions" overstates the number of genuine terrorists who have been taken to court. It would be nice if Congress actually took a serious look at this.
....Even some former government officials concede many intelligence investigations fail to yield evidence of a serious threat to the U.S. "Most of these threats ultimately turn out to be wrong, or maybe just the investigating makes them go away," said Washington lawyer Michael Woods, former head of the FBI national security law unit. "A lot more information is going to pass through government hands, and most of that is going to be about people who turn out to be innocent or irrelevant."