The NSA existing in a state that doesn't stop terrorist attacks is the status quo (it's the same as them not existing at all). It doesn't need proving.
If they want to spy on everyone in the world all the time and their reasoning is that it makes Americans safer, then the burden of proof is very much on them.
If they want to spy on everyone in the world all the time and their reasoning is that it makes Americans safer, then the burden of proof is very much on them.