No one has yet managed to explain how revealing that the administration illegally spies on American citizens without obtaining warrants, instead of legally spying on people after obtaining such warrants, damages national security.
Sure thing! Here’s Orin Kerr:
Finally, and relatedly, the details of the program from Risen’s book arguably explains the national security interest in keeping the domestic surveillance program a secret. It’s not that terrorists may suddenly realize that they may be monitored; that argument never made much sense, as every member of Al-Qaeda must know that they may be monitored. Rather, I suspect the security issue is twofold. In the short term, terrorist groups now know that they can stand a significantly better chance of hiding their communications from the NSA by chosing communications systems that don’t happen to route through the U.S. And in the long term, some countries may react to the disclosures of the program by redesigning their telecommunications networks so less traffic goes through the United States. The more people abroad know that the NSA can easily watch their communications routed through the U.S., the less people will be willing to route their communications through the U.S. Cf. Bruce Hayden’s comment. No doubt it was a long-term priority of the NSA to ensure that lots of international communications traffic was routed through the U.S., where the NSA could have much better access to it. Indeed, Risen’s book more or less says this. The disclosure of the program presumably helps frustrate that objective.
Hope that clears things up. (Oh, and I’m not even close to convinced that the program was illegal.)