I suspect that one of the strongest constraints upon an Administration decision, right now and perhaps for the time being, to strike Iran is not in the political realm, either diplomatically or with regards either to Congress or even public opinion, but from the military and from the intelligence services. There has been some very heavy opposition to Administration military plans, such as notions of putting up to 4 carriers in the Gulf (the 3-Star Admiral in the area put it almost bluntly to the Prez that there was no way more than 1 or 2 carriers were going to be in the Gulf and environs), and of course the intelligence services have been working hard to parry the Administration's thrusts for action against Iran for the past year or two (at least).
Um...isn't this more about the navy not wanting to commit too many resources in a restricted and restrictive battle space. Like putting them all in a bathtub. You could knock them out with a pea shooter. That's about strategic reserves, not about political policy.
With the release of the 2007 NIE and the Administration's unequivocal response to it, it really does seem that there is, or will soon be, the political will and the decision made, to deal with Iran in a manner that is intended to be decisive in its results - one way or the other. I think that other political factors have actually lost some of their potency, as it seems increasingly clear that the Adminstration, having had the Intelligence Services strip away an imminent justification for immediate action, nevertheless came right out anyway and all but say that Iran will be dealt with. The clock may already be set and time's running out. It may take a lot to stop this.
I've been thinking that all things are related and it is unlikely that we would have made these assumptions without other political and actual acts. NK pledges to shut down their uranium enrichment at Pyongyang and give US access to verify and dismantle. A nuclear site, either a reactor or weapons or materials, was bombed in Syria after Israeli fighters, probably with US assistance, negotiated the Russian made air defense system without one loss.

It is my position that our knowledge of this site and NKs involvement with the subsequent destruction, convinced NK to come to the table. Or, NK was in such bad economic and physical condition that they had to play ball and gave us the information and pledge for that assistance. Either way, it is likely that we gathered a lot more information on the nuclear situation in Iran and Syria and NKs involvement.