Graham Allison: "How Good is US Intelligence on Iran?"
... The current approach to Iran is predicated on the largely unexamined assumption that its overt enrichment program at Isfahan and Natanz is the problem and that a deal to freeze or dismantle the centrifuge facility constitutes a solution. The strategy doesn't address what US Secretary of Defense Donald Rumsfeld calls "known unknowns" - gaps in knowledge that have been recognized but not filled. [...]
Four huge "known unknowns" lie at the heart of judgments about the threat posed by Iran: First, is success in Iran's overt effort a necessary condition for success in its covert programs? Bush and his European colleagues operate on the assumption that it is. Otherwise their operational objective - a moratorium on research activities at Isfahan and Natanz - would be beside the point. ...