Since the government of Syria's Bashar al-Assad began to totter, the nonproliferation community has been waiting to see if he will unleash what is believed to be a large stockpile of chemical weapons, including VX, sarin, and mustard gas. The possibility that Assad might use chemical weapons is widely regarded as a possible trigger for U.S. intervention. In December, President Obama warned Assad of "consequences" in the event Syria used its chemical weapons. A few days earlier, Hillary Clinton warned that the United States was "certainly planning to take action" in the event of "credible evidence that the Assad regime has resorted to using chemical weapons against their own people." So, what makes for "credible evidence"? Enter Josh Rogin, reporter at Foreign Policy, who published a pair of stories detailing a State Department cable regarding possible chemical weapons use by Syrian forces in Homs. An administration official described the cable as having "made a compelling case that Agent 15 was used in Homs on Dec. 23." The implication, obviously, is that the "compelling case" is the "credible evidence" that should prompt Washington to rethink its policy limiting itself to "non-lethal" aid to Syrian opposition forces and take action. A reconsideration might be in order, though not for the reason you think. For starters, somehow, no one has bothered to mention that Agent 15 doesn't exist.