Why only in the late 70s the US received intelligence that the Shah has set up a nuclear weapons program. Thats what? 30 years ago? Good god, those Iranians sure work fast.
Then 1979 came, the revolution kicked out the Shah, the US stopped supplying enriched uranium and for a time nothing was mentioned about it, but surely they were still working on it n secrecy right? Right?!
I mean there is no other explanation as to why in 1984 when the Bushehr reactor was still unfinished West-german Intel claimed they are almost there.
Then in 1992(by that time weren't they supposed to have nukes? It seems the quality of the cold and calculating german mind is not what it used to be) Israel claimed several times that Iran is trying to get nuclear weapons, or almost there, or will get them in a few years. The USA joined in the chorus, crying Wolf! for the better part of the decade, outlets like the New York Times or Christian science monitor giving them anything from 5 to 10 years until they finally have The Bomb.
After 9/11, Iran was labelled part of the Axis of Evil(why nobody asked them on their opinion? What if they wanted to call themselves the Justice League or Legion of Doom or something? So very rude...) and their nuclear abilities were put on par with North Korea(which supposedly managed to get the bomb by now).
After the dust was settled on the Iraqi battlefields, the saber rattling increased progressively with each year. Bush claimed a nuclear Iran could lead to WW III (might be true, question is - who will start it hmmm?) Dick Cheney waved his finger too, but with both of them soon to be out of office, the heat was toned down a bit.
But in 2010-2011 things heated up. A nuclear Iran was called the greatest threat to the survival of the jewish people since Hitler(I think we should make a measurement unit from his name, like Newton, Watt, etc. but it will be used to describe honestly bad people or simply those who say Israel should tone down on the bombing of Palestinians."Nah he's small fry - only 0.01 hitlers on my reading".) A good number of reports came out with all sorts of timeframes - from 6 months to 5 years to tomorrow.
Aaaand that brings us to present day, when Iran is more or less juuust about to get the bomb. Again. They are probably right too. I mean come on -they've been at it for 3 decades...