The longer term damage may be more real. Foreign governments may think twice before sharing their secrets or even their candid judgments with American counterparts lest they read about them on the Internet. And American diplomats may be less less willing to commit their thoughts to paper. Such reticence will deprive policymakers of an important source of information and make decisonmaking more ad hoc and less systematic than it needs to be.
I've spoken with three ambassadors today already, and all of them said their governments were shocked by America's inability to keep its secrets secret. One ambassador said, jokingly (but only half-jokingly), "Do you think Putin would have let this happen?"
Putin would not have let this happen, which is why I'm glad I live in the U.S.