Iran today has reached a status I have long dreaded: It operates a semi‐industrial‐scale uranium enrichment facility and is building up a stockpile of enriched uranium that is of no current use to its civil nuclear energy program but that could be put to weapons purposes. Meanwhile Iran is also building a research reactor that will be ideal for producing plutonium – the other path to nuclear weapons.Whether or not Iran chooses to go down the weapons route, its persistence in developing such capabilities could have profoundly disturbing consequences, including by potentially sparking a proliferation cascade in the Middle East and beyond.