Isikoff implied that a "classified State Department report" may be the smoking gun. This classified document is referenced in several news articles starting in October 2003 and is the probable source "for the information that Rove and others were then dishing out to reporters".  

Powell had this document with him on the trip to Africa that occured right after Wilson went public in his July 6th 2003 op-ed. The Africa trip was from July 7th through July 12th.

I believe this document had been prepared in advance to be ready to use if Wilson spoke out. Wilson was leaking, he was clearly the source for several articles in May and June of 2003 (links are provided below) . The White House was ready to push back and this classified document was the evidence. The main talking point the White House decided to use to discredit Wilson was that Plame was involved in setting up his trip to Niger.

ISIKOFF:

That classified State Department report appears to have been -- or may well have been the source for the information that Rove and others were then dishing out to reporters. And if that's the case, there still may be -- we don't know yet, but there still may be an instance where classified information was provided to reporters.

Reference to this classified document first turns up on October 17,2003 in the Wall Street Journal.

more..