As difficult as forging an agreement will be, there is considerable value in having clarified what stands in the way. It would be as grave a mistake to underestimate how far the negotiators have come as it would be to overestimate their chances of success. Obstacles notwithstanding, there is a credible path to an agreement. It would require for Iran to postpone its plans for industrial-scale enrichment while the P5+1 countenances controlled growth of that program and clearly defines target dates for a phased lifting of sanctions.