This in spite of the fact that the US intelligence community is fairy unanimous that Iran is not even currently pursuing nuclear weapons. According to Micah Zenko:
First, as Director of National Intelligence James Clapper has repeatedly reaffirmed since late January, "we don't believe they've actually made the decision to go ahead with a nuclear weapon." Just yesterday, James Risen reported in the New York Times that the IC continues to believe (based on an assessment first made in November 2007) that Iranian Supreme Leader Ayatollah Ali Khamenei halted his country's nuclear weapons activities in 2003.So 60% of Americans believe Iran should be attacked to prevent nuclear proliferation. Simultaneously 71% of Americans - in total contradiction to the evidence recognised by both the CIA and Mossad that Iran is not currently even developing a nuclear weapon - believe that Iran currently has nuclear weapons. There is almost certainly a high degree of overlap - and that's some severe cognitive dissonance. Where are such ideas coming from?
This might be hard for many to grasp, since polling has found the American people disagree with the collective judgment of the 210,000 civilian and military employees and 30,000 private contractors comprising the IC. A recent poll found that 84 percent of Americans think Iran is developing nuclear weapons, while another from February 2010 concluded that 71 percent of Americans believe that Iran currently has nuclear weapons.
There are some voices in the wilderness that are expressing the view that Iran already has a nuclear weapon to anyone who will listen.