Dan Drezner writes :
Take the “deal or war” perspective. The prospect of the U.S. having to use air power against Iran does sound pretty bad. Well, it did sound bad, back before the U.S. was using air power in Iraq. And Syria. And providing support for others to use air power in Yemen. And lengthening the stay of U.S. forces in Afghanistan.
When you think about it that way, does adding another country to the bombing list really matter all that much? [bold mine-DL]
The answer, from a foreign policy perspective, is that of course it does. Bombing Iran is an order-of-magnitude difference that what the U.S. is doing in Iraq, Syria and Yemen. But my point is that the optics of greater U.S. use of force in the Middle East doesn’t look as problematic as it did, say, in January 2014. The disastrous counterfactual does not look too far removed from reality.
Well, yes, it does matter quite a bit. A war with Iran would be a huge change for the worse for the entire region, and would be a major new burden for the U.S. to take on. If the region appears horribly chaotic and violent now, it might seem hard to imagine how it gets worse, but bombing Iran would make us see how much worse it can get.
For one thing, there are the U.S. forces present in Iraq and Afghanistan that could be attacked in reprisals by Iranian proxies if the U.S. “added” Iran to “the bombing list.” The air war against ISIS stays out of the headlines and remains popular here in the U.S. because it doesn’t involve any American casualties. The U.S. also has at least the nominal approval, if not support, of the rest of the world in fighting ISIS. War with Iran wouldn’t be like that. It would be much more costly and dangerous for U.S. forces, and it would be an illegal war condemned all over the world. Attacking Iran would invite retaliation against U.S. forces and clients in the Gulf, and according to the Iran hawks that argue for bombing this would just be the start of a series of attacks on Iran. That would destabilize the region even further, and it would turn the Persian Gulf into a war zone with negative consequences for the global economy. Robert Farley describes  this scenario:
And the core argument is this: the United States should regard itself on more or less permanent war footing with the Islamic Republic, and should expect to regularly use air and sea power in order to curtail Tehran’s ambitions.
If the United States launches a major strike on Iran, it can expect to launch another strike in a few years, and another strike a few years later. Each time, Iran will improve the security of its nuclear facilities, and each time, it will build sympathy within the international community.
Attacking Iran’s nuclear facilities would be the beginning of a new open-ended military commitment and the start of a prolonged war with Iran whose effects will probably surprise us by being even worse than we imagined beforehand. On top of all that, it is likely that such a “preventive” war wouldn’t stop Iran from acquiring nuclear weapons, but would virtually guarantee that outcome. As Geoff Wilson explained  over the weekend, attacking Iran would just drive their nuclear program deeper underground. Iran hawks like to invoke Osirak as proof that military action can halt another country’s nuclear program, but Wilson reminds us that the attack on Iraq in 1981 produced the exact opposite result:
Both Bolton and Cotton’s accounts of the strikes on Iraq in 1981 are completely wrong.
Those strikes actually drove the program underground, where it expanded. This is just what Gates warns would happen with Iran. As Deputy National Security Advisor Colin Kahl wrote in 2012, “new evidence suggests that Hussein had not decided to launch a full-fledged weapons program prior to the Israeli strike.”
So in addition to making the region’s problems even worse, the war would likely produce the result it was intended to stop. I understand that Drezner wants to make advocates of both positions reconsider their arguments in light of regional events, but regional instability and U.S. involvement in these other conflicts make the awful case for starting a war with Iran seem far worse than it already did. If a quarter of a neighborhood is already on fire, that doesn’t make setting the rest of it ablaze any less abhorrent or foolish.