It's obvious to me from the President's comments today that he believes the leak came from Capitol Hill. That's why he sounded so strident about that as well as about the Patriot Act. I think it may have finally dawned on him that we really do have some treasonous traitors in the U.S. Senate.
It seems that it wouldn't be that hard to figure out. Not many people have this top secret info. Start with the democratic and Republican senators on the Intelligence committee and go from there. Shouldn't be too hard.