Iran probably has the where-with-all to assemble a bomb within a few weeks (they had this capability for several years, according to the Israelis and CIA). All they are doing now is manufacturing more enriched uranium and plutonium for more bombs. Other countries have nuclear weapons as well, including China, India, Pakistan, North Korea and, (surprise) Israel.
True, the US is negotiating with Iran to curtail or control its nuclear program, but we have little real influence over them. Sanctions have hurt, but they've successfully continued with their program. What else can we do, short of war?
I don't believe that the US and the rest of the world really want a war with Iran, it would be bloody, expensive and inconclusive (just as the wars in Iraq and Afghanistan have been). Iran's nuclear facilities are deeply underground, buried deep into mountains (consider Cheyenne Mountain in Colorado - it is designed to withstand a nuclear attack).
So you make the best deal you can and continue monitoring the situation for 10 years or so and then reassess, as required. Not much else that can be done.
