Spy v. Spy
So why isn't the headline, "Secret NSA Wiretaps Led FBI to 'Potential Terrorists"? I don't know what a potential terrorist is, but it seems pretty clear that the NSA program turned up at least one. It seems like the FBI sources are attempting to attack the wiretap program on bureaucratic and pragmatic grounds: Screw the Constitution, it's a waste of time and shoeleather anyway. But that's a very tough argument to make, because all you need is one good hit to justify all the effort. And the FBI obviously can't make the case that zero good leads have emerged, or you wouldn't have all that ass-covering language attributed to counterterrorism sources.
Of course, if you oppose the illegal wiretaps, as I do, you have to be willing to do so even if they work. Their utility or efficacy shouldn't enter into the argument.