Because good old Joe said so in his op-ed piece
http://foi.missouri.edu/terrorintelligence/whatididnt.html
Though I did not file a written report, there should be at least four documents in United States government archives confirming my mission. The documents should include the ambassador's report of my debriefing in Niamey, a separate report written by the embassy staff, a C.I.A. report summing up my trip, and a specific answer from the agency to the office of the vice president (this may have been delivered orally). While I have not seen any of these reports, I have spent enough time in government to know that this is standard operating procedure.