If President Obama really manages to pull together a deal with Russia that cuts each country's stockpile of nuclear warheads by four fifths it will be an astonishing feat, and one that will give him a claim to have set US foreign policy on a very different course.
The time is right. The present arms deal runs out at the end of this year. Both countries have far more warheads than they need for deterrence and could do with saving money (this is an understatement) from that part of the defence budget. It would also put the US in a far stronger position to argue against nuclear proliferation -- in Iran, in North Korea, and across the Arab world, where leaders have shown quiet interest.