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Everyone wants a silver bullet to resolve America's policy dilemmas in dealing with Iran and its nuclear ambitions. Unfortunately, none of the popular candidates"”engagement, military action, sanctions or regime change"”seems sufficiently likely to succeed to be the basis of prudent government policy when vital U.S. national interests are at stake. Instead of hoping for a silver bullet that will make the problem go away, or at least push it down the road, policy makers should start to develop a serious plan to manage the most likely future: an unreformed and nuclear-capable Iran.

The United States has tried and failed many times at engagement with Iran. The attempts have generally been necessary and appropriate, but as Tehran continues to move forward with its...