Matt Stoller does an interview:
Matt Stoller: Can we handle a nuclear Iran? Can we live with that?
Wes Clark: I don't think so. The reason is, there are three reasons. Number one is that I think a nuclear armed Iran would use its clear deterrent to promote conventional or unconventional aggression against other states in the region and believe it could sit back with its nuclear power and not be threatened in return. I think the second reason is you never know how these nuclear capabilities might be smuggled abroad or used in some way. Maybe the way we saw the Israelis strike at this nuclear depot in Syria is an indication of that and apparently that came from North Korea. And the third reason is that once Iran gets a nuclear weapon lots of other countries will want them and the more countries that have them the greater chance a nuke will be used and kill hundreds of thousands of people and so no I don't think you can tolerate a nuclear armed Iran. But I think the right course of dealing with it is to directly engage Iran in dialogue.
The weird thing here is that I totally agree with Clark's analysis of what would be problematic about an Iranian nuclear weapon. This just seems like a strange conception of something we can't live with. The prospect of the Red Army overrunning Western Europe was something we couldn't live with. We formed NATO, provided explicit defense guarantees to our allies in the region, stationed troops in Germany, Italy, Turkey, and Britain and were prepared to wage warfare on a truly massive scale -- just as we had during World War II -- to prevent the domination of Europe by a hostile totalitarian power.
Iran having a nuclear weapon would be bad, for the reasons Clark adduces, and it's worth trying to prevent in just the way he suggests. But one shouldn't suggest that it's some kind of intolerable threat to American security or that we'd have no way to cope with the consequences of an Iranian nuclear weapon. It's just a scenario we'd prefer to avoid.