The NSA stops lots of terror attacks.
Why do you think they do not?
The FBI was present during the Garland attack and they did nothing to greet the terrorists going there. Suspicion is that the FBI was surveilling Pamella Geller’s event on orders of outfits like SPLC, Obama’s Muslim Brotherhood or Mueller’s old guard and to do nothing of the terrorists going there.
Bottom line is they have the datas on this sht and they never stop it.