This past Friday, the architect of the Iranian nuclear program, Mohsen Fakhrizadeh, was assassinated in a well-organized raid 70 km outside the city of Tehran. A commander of the Islamic Revolutionary Guard Corps (IRGC), Fakhrizadeh headed the important Organization of Defensive Innovation and Research of the Ministry of Defense, which conducted nuclear weapons research. His killing reflects a major breach in Iranian counterintelligence and could indicate that the regime’s intelligence and security apparatuses have been compromised. Iran will have to respond to Fakhrizadeh´s assassination, but will likely do so in a manner that avoids full-scale war.