Politicians from both parties and a variety of countries like to talk as though we have multiple options with Iran, that we can prevent them from getting nuclear weapons by force or coercion. Here’s a map.
See those countries on the top and bottom of the map of the Caspian Sea, a sea in which the US has next to no military presence? Iran doesn’t have nuclear weapons or fissile material for one reason – Russia doesn’t want them to have them. There are two likely reasons for this:
1. Russia likes to have Iran threatening the West, but doesn’t want Iran to have power in its own right;
2. Giving countries, even your allies, fissile material is seriously frowned upon in the international community.
The maintenance of these two rationales needs to be the centerpiece of American foreign policy vis-a-vis Iran. Invading Iran would invalidate both of them. Indeed, any kind of aggressive behavior by the US would reinforce the idea that Iran needs nuclear weapons for self-defence, and weaken the moral or legalistic non-proliferation arguments that could be used against Russia should Iran happen across a couple bombs worth of enriched Uranium. I don’t think Russia wants Iran to have nuclear weapons, but I can absolutely see the reasoning that would lead Russian leaders to decide that a nuclear armed Iran is needed to keep the peace (and remember, we created this world when we invaded the belligerent but non-nuclear Iraq but left nuclear-armed N. Korea largely alone).
What, then, must we do? In the short term, we can’t give Russia any reason to change its belief that Iran doesn’t need nuclear weapons. In the medium turn, we need to convince Iran that it doesn’t need nuclear weapons. That means letting Syria peacefully destroy its chemical weapons and not intervening militarily there. That also means eventually normalizing relations with Iran, the first step of which is lifting sanctions in a tangible way, and moving away from a policy that centers around the needs and desires of Saudi Arabia and Israel to the detriment of the rest of the Middle East.
The Right will say this amounts to appeasement, that somehow Iran is Germany and we are the UK at Munich. But they have it wrong – there is no way to strong arm our way to a more peaceful middle east. There is a much better analogy in European history the early 1910’s. We are Germany, Iran is Serbia, and Russia is, well, Russia (if you want, Israel or Saudi Arabia can be Austria-Hungary). Iran represents almost no threat to us except as far as they can draw us or our allies into open conflict. It is imperative that we make clear that we are not going to let national machismo or misplaced fear prompt us to do something disastrous for both sides.