How much Iranian nuclear capability is too much? The simplest answer is that any amount is unacceptable. By learning how to enrich uranium, Iran has given itself the potential to eventually produce enough weapons-grade material for one or more atomic bombs. That risk can only be removed if all Iranian enrichment programmes are eliminated. This belief has long been a mainstay of U.S. rhetoric, if not policy, towards Iran.
But it is far from clear that zero enrichment is a realistic goal. Indeed, despite recent setbacks, Iran's leaders appear determined to continue improving and expanding Iran's enrichment programme; they may even have already decided to eventually build a bomb. The important question, then, is how much Iranian nuclear capability is too much, given the limited (and often costly) options available for curbing Iran.
It is thus essential that U.S. and other strategists, policymakers and negotiators understand the consequences of different possible states of Iran's enrichment programme. These can be grouped into four basic categories. The first is zero enrichment, which is still the official goal of the United States and other UN Security Council members. The second is limited enrichment, in which Iran has some non-trivial enrichment capability, but is unable to produce a bomb (or small arsenal) without risking strong international retaliation, including military destruction of its enrichment infrastructure. Holding Iran to this level appears to be the goal of current US policy, even if it is not typically articulated this way. The third category is robust enrichment, in which Iran is capable of producing a bomb (or small arsenal) without significantly risking strong international retaliation aimed at preventing it from completing that task. In this category, Iran still does not actually have the bomb, but is genuinely ‘nuclear capable' (or can be said to have a ‘robust breakout capability'). The final category is a nuclear-armed Iran.