Noah Millman makes  some good points on the need to have realistic goals for what diplomacy with Iran can accomplish:
Our goal is not “flipping” Iran from the enemy to the allied column. We should not be surprised or offended if Iran continues to posture against America in international forums, or even take more concrete actions to frustrate our aims in the region. We should expect them to want to drive a wedge between us and our allies, and to spin any agreement as our defeat [bold mine-DL]. We should keep our eye on our primary objectives. Our goals are avoiding war and neutralizing the destabilizing threat of Iranian nuclearization. Their goals are avoiding war and ending the sanctions regime. We have concrete goals and interests, and so do they. That’s what we should be talking about – and getting to a deal on. If love follows in its season, well and good. But we don’t need it.
I would add that the most successful negotiation between the U.S. and Iran might be one that results in an agreement that both governments can sell to their respective hard-liners as a national victory. As appealing as rhetoric about moving beyond “zero-sum” relationships may be, an enduring deal between the U.S. and Iran probably has to be one that placates enough hard-liners in both countries, and that could mean portraying the deal as a loss for the other country. As desirable as full rapprochement with Iran  would be, that will likely have to wait for a later time. A deal on the nuclear issue can become the foundation for later rapprochement, but it doesn’t have to produce the latter in order to be successful on its own terms, and it shouldn’t be judged by whether rapprochement follows from it.
Millman is right that Iran doesn’t want to be brought into the “fold” as a client of the U.S. Iran wouldn’t want that kind of relationship, and most American policymakers wouldn’t want it, either. Iran does want the U.S. to stop treating it like a pariah, and the U.S. should want to establish normal ties with Iran. If there is a model for how a U.S.-Iranian relationship could develop in the future, I suspect it would be more like the normalization of relations with Vietnam that are now almost twenty years old: improving diplomatic and economic ties with a previously hostile regime that doesn’t change its internal political system very much.