There is some subtlety to this position and it probably reflects reality - to a point.

Since we are unable to look into the minds of the Iranian leadership, we can't say with any degree of certainty that their intent is to build a nuclear bomb. Public statements about "wiping Israel off the face of the earth" by Ahmadinejad - a man who will not have the final say in any attack on Israel - are instructive but hardly proof in the sense that our intelligence experts can't inform policymakers with any certainty that the threats are based on reality.

What we do know, is that they are assembling the hardware, the know-how, and technology to build a nuke if they choose.

LA Times:

A highly classified U.S. intelligence assessment circulated to policymakers early last year largely affirms that view, originally made in 2007. Both reports, known as national intelligence estimates, conclude that Tehran halted efforts to develop and build a nuclear warhead in 2003.

The most recent report, which represents the consensus of 16 U.S. intelligence agencies, indicates that Iran is pursuing research that could put it in a position to build a weapon, but that it has not sought to do so.

Although Iran continues to enrich uranium at low levels, U.S. officials say they have not seen evidence that has caused them to significantly revise that judgment. Senior U.S. officials say Israel does not dispute the basic intelligence or analysis.

But Israel appears to have a lower threshold for action than Washington. It regards Iran as a threat to its existence and says it will not allow Iran to become capable of building and delivering a nuclear weapon. Some Israeli officials have raised the prospect of a military strike to stop Iran before it's too late.

Isn't that enough, you might ask? For Israel, yes. They have a far lower threshold for allowing the Iranians the luxury of getting all their nuclear ducks in a row - and then being capable of assembling a bomb in a matter of weeks or months.

President Obama has been very careful in saying that we would not allow Iran to build a weapon. In other words, until we have conclusive evidence that Iran isn't merely preparing to build a bomb, but is actually constructing a weapon, we will take no action.

Is this a political consideration and is the NIE a political document? Of course. The report dovetails nicely with exactly what the president wants to hear. But the document is a consensus paper, passed around to 16 agencies who give their own slant and perceptions on the raw intelligence. It's bound to be a little mealy given the compromises that go into the issuance of such a report.

What might change this calculus is the discovery of a secret facility that connects all the dots and proves Iran's intent. Some Iran hands at CIA believe there to be one or two such facilities buried deep underground somewhere. Until we find such evidence, our intelligence people will continue giving policymakers cautious, realistic - and political - assessments of what is going on with the Iranian nuclear program based not on emotion or supposition, but on consensus conclusions reached by a wide variety of government offices.