Would they? Able Danger's data-mining seemed to be working but they weren't allowed to share. I hope the FBI would be investigating. But I also don't believe that we should rule out any options in this war.
I was simply responding to the assertion in the header of this article that authorizing the taps of suspected terrorist conversations was inadequate in terms of surveilling domestic terror groups. That's not the NSA role. I'm sure the FBI and other domestic police organizations are working in that area.