One of the few things about which I agree with both President Bush and my father: despite December's NIE report which stated with high confidence that Iran halted its nuclear weapons program in 2003, Iran remains a threat. According to a Newsweek article, President Bush told Israeli Prime Minister Ehud Olmert that the NIE's conclusions don't reflect his own views, but I think that there is plenty of evidence in the NIE report to support Bush's view that Iran is still a persistent threat.
The first sentence of the Key Judgments section of the NIE report reads as follows: "We judge with high confidence that in fall 2003, Tehran halted its nuclear weapons program; we also assess with moderate-to-high confidence that Tehran at a minimum is keeping open the option to develop nuclear weapons." Everything before that semicolon is what we've all heard from the press; everything after the semicolon is what we hear from President Bush. In reality the President's assertion that Iran is still a threat despite halting a nuclear weapons program in 2003 is clearly laid out by the very document that Bush has "all but disowned".
Iran's actions prove that they have every intent on continuing to enrich fissile material. Iran continues to thwart the International Atomic Energy Agency inspectors and the United Nations by continuing to enrich uranium. They have opened at least one new enrichment facility in the past year, and they continue installing centrifuges at their facilities. Iran claims that the enrichment of uranium is only for peaceful nuclear power. This may be true or it may not be, but it certainly shouldn't matter to us. The difference between civilian-use enriched uranium and weapons-grade enriched uranium can be made up with a few more spins around the old centrifuge. Plus, also according to the NIE report, "Iran has the scientific, technical and industrial capacity eventually to produce nuclear weapons if it decides to do so."
So the only reason why Iran can't develop a nuclear weapon right now is because it takes a really long time to separate out enough U-235 from the uranium ore to make enough fissile material to go to critical mass. There is a miniscule ratio of naturally occurring U-235 to U-238, and the weight difference is also miniscule, so it takes many chains of centrifuges and many years of spinning in order to get a small amount of the stuff. During WWII, the United States worked non-stop day-and-night from 1942 to 1945 on developing enough U-235 to create one bomb. After dropping our one uranium bomb and our one plutonium bomb on Japan, the threat was something like, "Surrender now, or there's more where those came from!" Complete bullshit of course, as it would have taken another couple of years just to get enough fissile material, but the threat worked and Japan finally surrendered. My point is that it's not a lack of technological knowledge that's keeping Iran from having a bomb right now, it's a lack of materials. And the soonest Iran could get enough U-235 would be about 2010, and the soonest Iran could get enough plutonium would be about 2015, according to the NIE report.
In addition to saying that the uranium enrichment is for civilian power facilities only, Iran has also declared that they never had a nuclear weapons program, which of course the NIE refutes. So, Iran tells the truth only when it wants to and closes its doors to the West. Even if Iran is telling the truth about their civilian enrichment program, there's no reason to believe them.