To my mind, the FBI, CIA, NSA, DHS or the TSA has never provably stopped a terrorist action BEFORE it happened.
We often hear how they have prevented this and that, but they are lies, frankly, often with background lies that cannot be substantiated because of dubious claims about operations in foreign countries.
What about the attempted bridge bombing, just South of Cleveland?
Old joke:
How do you identify the FBI agent at the Klan meeting?
He’s the one with the dynamite.