Aaron David Miller believes that the desire to pursue diplomacy with Iran has been an important factor in Obama’s Syria policy:

Yet there is one reason for the president’s caution that he almost never mentions — and it may be one of the most compelling. Not surprisingly, it is derivative of Obama’s most important foreign-policy objective in the Middle East: a nuclear deal with Iran.

It’s an interesting idea, but I’m not sure it holds up. I agree that attacking Syria would have made it much more difficult to pursue diplomacy with Iran, especially if Iran had reacted to an attack by striking at U.S. or or other targets in the region. It’s not entirely a coincidence that the decision not to attack Syria was followed by progress in talks with Iran. Contrary to what many Syria hawks said at the time, using force in Syria was exactly the wrong thing to do if the U.S. wanted negotiations with Iran to have a decent chance of success, but there is not much evidence that administration officials understood this. Even so, if the administration’s Syria policy had really been so constrained by a desire to reach a deal with Iran on the nuclear issue, it is hard to believe that Obama would have ever seriously contemplated military action in Syria in the first place, much less made a concerted effort to sell Congress on the merits of its proposed “limited strikes.”

The administration may have been wary of launching an intervention on a large enough scale that it would provoke Iranian retaliation, but in their public case for attacking Syria administration officials deliberately minimized the danger of an Iranian response. Before the spectacle of the administration’s push for military action last summer, it might have made sense to think that U.S. restraint in Syria was driven by an interest in resolving the nuclear issue through diplomacy, but that doesn’t hold up very well now. As it turned out, the administration dodged a bullet that it had fired at itself, and this happened mainly because of overwhelming public and Congressional resistance to the ill-conceived proposal to attack Syria. Last year, Obama’s muddled Syria policy was on a collision course with U.S.-Iran diplomacy, and it was really only because his proposal to use force in Syria was vehemently rejected by the country that this collision was avoided.