I was just having an email discussion with a friend who was incredulous at Jewish support for the Iran deal and for supporting Obama's efforts there. Here was my response:
I said at the time, and I still believe this, that yes, the Iran deal was a bad deal. But that's because any deal with Iran would be a bad deal. There was no possibility of a good deal. So the question becomes, was a bad deal better than no deal at all? I tend to lean towards answering yes. The deal wasn't meant to be an absolute guarantee that Iran wouldn't develop nuclear weapons, it was meant to slow down that program dramatically, and at the same time bring a rogue nation into the sunlight of international diplomacy, which would gradually move them towards some kind of relative moderation. Simply ostracizing them would have caused them to work harder to get a bomb and they wouldn't have much to lose by threatening its use later.
You can disagree with Obama's reasoning, but he wasn't just being naive - he had a method to what he was doing, the belief that diplomacy, even in the cases where such diplomacy will be tough and take years, is the only thing that will guarantee peace in the long term. I agree with that approach, even if I sometimes disagreed with Obama on details.