Just to add to Tom Joscelyn's excellent post on the National Intelligence Estimate, Cliff May offers this note from a former CIA insider:

[While this NIE] does confirm Iran was pursuing nuclear weapons in 2002 and 2003, its conclusions that as to why it may have stopped the program and why this halt may have continued are debatable [sic] and speculation. These KJs [Key Judgments] have too much political spin. This assessment was strongly influenced by two hyper-partisan anti-Bush officials who oversaw it, both former State officials who fought tooth and nail against Bush WMD policies, especially Iran.

I've heard similar rumblings from similar people, though less specific.

While I do agree that the NIE was somewhat less grounded than previous estimates, I don't agree with what is becoming a popular conservative talking point: Iran dropped their program in 2003 because OIF showed the world that America meant business. I think that it's far more likely that the Iranians--if they really did drop their program--had a North Korea (rather than Libya) style epiphany, realizing that the technological hurdle in constructing a bomb, shrinking it, and mating it to an effective delivery system was just too complicated of an endeavor. Had Iran truly been scared into submission by the U.S. invasion of Iraq, I doubt we would have heard four years of blustering about "Iran's right to nuclear research and development" and boasting about "thousands of operational centrifuges."

But that doesn't mean that liberals are being any more rational. It's amusing to watch the transformation of the most ignorant left wing bloggers into defense experts every time an ideologically satisfying Pentagon/CIA press release appears, but any discussion about how the NIE is a blow to the Bush administration's plan to attack Iran is just silly. For one, the NIE's confirmation of Iran's nuclear intentions prior to 2003 completely justified the White House's relatively measured "all options are the table" rhetoric, and second, the White House has never deviated--nor threatened to deviate--from its commitment to a diplomatic resolution. And to clarify, no... acknowledging that military options exist is not a deviation from diplomacy. Executing a military option is a deviation from diplomacy.