A few dozen times.
Then there's an attack, and the President gets to lecture us about weakening security. Then everybody hangs their heads and lets the agencies do whatever they want again.
I personally believe our representatives in Congress are terrified of being the one blamed for weakening our security.
(Yeah, that would never happen...)
Most recently, the shooting at Garland, TX. It seems the FBI knew about this ahead of time, and did a spectacularly bad job of warning the local authorities. But the attack was averted anyway, and according to the police chief there...
What does this all mean? Not much says Police Chief Bates, "Please note that the contents of that email would not have prevented the shooting nor would it have changed the law enforcement response in any fashion."
http://www.npr.org/blogs/thetwo-way/2015/05/11/406025002/tex...
There's an enormous world of difference between those two things.