I've read all Mowbray's reporting on this issue, and he has not revealed anything that could be considered injurious to our national interests. On the contrary, he has shown the light of day on a culture that places its interests above Americans' security. It sounds like he was naive, or perhaps frustrated, enough to make a mistake in this instance, but I have a feeling the so-called "cable" contained nothing more than further embarrassing information about the State Department's handling of visas. State has outright lied and ducked about this issue for months, and what is obvious from Mowbray's writing is that there are people within the department who are just as outraged by the policy as he is.
My hunch is that the cable was classified CONFIDENTIAL or the innocuous Official Use Only, or they might have really made trouble (which is what they wanted to do in the first place). Now State has undoubtedly got the original and there are markings on some cables that can give away its provenence. Let's hope he hasn't blown his source. I still say it is likely that he will lose his State pass privilege, because if for no other reason, he should have known better than to sound off the way he did