The Wall Street Journal reports that an attack on Syria would likely wreck negotiations with Iran:

A U.S. attack on Syria would likely dash expectations of progress in nuclear negotiations with Iran and undermine new Iranian President Hasan Rouhani’s call for improving relations with the West, diplomats said.

This is one of the problems with an attack on Syria that I mentioned yesterday. When the U.S. was declaring its intention to arm the Syrian opposition, it seemed that this could derail any attempt to reduce tensions with Iran. A direct attack on Syria would make it virtually impossible for Rouhani to pursue a more conciliatory course, which in turn makes conflict with Iran more likely in the coming years. Iran might not respond militarily to an attack on its ally, but if hard-liners in Tehran are as blinkered as our own “credibility”-obsessed politicians they very well might feel that they have to respond or risk being perceived as weak. Whether Iran retaliates or not, Rouhani will be in no position to offer concessions, and Iran hawks here will use this to justify their own demands for even more sanctions and more aggressive measures against Iran’s nuclear program.

One of the more curious things about arguments for intervention in Syria is that most of them have focused on Iran’s support for Assad as a reason to enter the war, but they never consider the possibility that Iran could strike against U.S. interests or clients in response. Most Syria hawks think that using force against Assad will prove to Tehran that the U.S. is serious when it makes threats against other governments, but they assume that hard-liners in Tehran will react to an attack on their ally by becoming more accommodating, which is the exact opposite of what they themselves would do if a U.S. ally were attacked. Most Syria hawks have tried selling war in Syria as a way to avoid war with Iran, but with each step towards direct military intervention in Syria war between the U.S. and Iran is becoming more likely.