At some point, I believe, they will stand before us and claim that conventional weapons can't do the job, so they'll just so happen to need to begin production of new nukes.
They need a place to use as an antagonist since Saddam isn't there for them to lie about. They've got Iran to pose as the threat, the evil, that they need to justify their meddling.
I don't think this is as much about Iran, as it's a convienience to have part of Bush's 'evil axis' and the legend of these underground bunkers to serve as an impetus for their meddling with the existing arsenal. That's something they haven't mustered the gravity for up until now.
No enemy with a deep underground target? No need for new, nuclear 'bunker-busters', and no need for new nuclear weapons production plants with the "capacity to produce 125 nuclear bombs a year".
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