There are a number of bad precedents there, not least being that US policy toward North Korean nukes since they actually tested one has been useless whichever party held the White House. I still get the impression that a country without nukes (e.g. Iraq) is vulnerable but a country able to hold us or our allies nuclear hostages (e.g. North Korea) is not. But more importantly, I don't think I'm the only one who sees it that way.

As for Toms point on the terror of increased sanctions, I'm not convinced. As long as China threatens a veto (and as long as they're playing nuclear arms dealer to the world they will) the US can only act unilaterally, so there will still be plenty of places Iran can get what they want. Might cost more, but they'll get what the regime requires.