While you would never know it from mainstream media coverage, the U.S. officially remains unconvinced that Iran is actually seeking to build a nuclear weapon. And no one in the U.S. military actually believes that Iran would ever adopt a first strike policy even if it did have a weapon. In short, the U.S. does not accept Israel's insistence that Iran is an "existential threat" to Israel
"Nuclear weapons are not at all beneficial to us. Moreover, from an ideological and faqih [Islamic legal] perspective, we consider developing nuclear weapons as unlawful. We consider using such weapons as a big sin. We also believe that keeping such weapons is futile and dangerous, and we will never go after them. They know this, but they stress the issue in order to stop our movement." [-- Ayatollah Ali Khamenei, Iran's supreme ruler]
Read the whole article: Is Stephen Harper Undermining Obama on Iran? » Counterpunch: Tells the Facts, Names the Names.