During the early Bush administration, it was said that any uranium enrichment at all by Iran would be considered an unacceptable threat. Then it was said that enrichment beyond a certain percentage of refinement would be unacceptable. Then in 2007, a National Intelligence Estimate loosened the definition of threat even further, declaring that “by ‘nuclear weapons program’ we mean Iran’s nuclear weapons design and weaponization work.”

And now the Obama administration seems to have decided to draw the line at a decision by Iran to actually begin the assembly of a bomb. There is no shortage of evidence that this is the new working definition. The Washington Post recentlyquoted a senior U.S. official as saying, “There is confidence that we would see activity indicating that a decision had been made.” In January 2012, Director of National Intelligence James Clapper told the Senate Select Committee on Intelligence that “they are certainly moving on that path, but we don’t believe they have actually made the decision to go ahead with a nuclear weapon.” Secretary of Defense Leon Panetta told the Senate Budget Committee that “our intelligence makes clear that they haven’t made the decision to develop a nuclear weapon.”

This latest red line makes eminent political sense, in that it would certainly forestall the triggering of military intervention until after the coming presidential election. But from a security viewpoint, as well as that of decision-making theory, the new threshold is a catastrophe.