It is amazing to me that more countries do not have nuclear capabilities. This was a technology that the USA developed almost 70 years ago. I have a book on my shelf, The Making of the Atomic Bomb by Richard Rhodes that pretty much lays out how to a nuclear explosion is achieved.
The hard part is not making a crude working bomb, but getting enough refined fissile material.
The longer we/Israel gives the Iranians the more uranium ore they can refine into U235.
It's highly unlikely they could launch anything against the U.S. unless maybe right off the coast in international waters from a oil tanker or cargo ship with little time to intercept.
Second only to Israel, Iran hates the U.S. and wouldn't hesitate to do something really really stupid.