It looks like President Obama has decided to make the Nuclear Non-Proliferation Treaty the key to his new nuclear strategy, by pledging that the United States won't use nuclear weapons to respond to an attack by a country that adheres to the treaty. That would be a significant shift from the Cold War nuclear posture, and it would heavily tie the future of U.S. nuclear weapon strategy to global efforts against nuclear terrorism and non-proliferation--and would disentangle years of history and culture that link American nuclear weapons use to other countries--"state actors," in nuclear parlance.
The New York Times reported that President Obama, in an interview with the Times, said that the U.S. is "going to want to make sure that we can continue to move towards less emphasis on nuclear weapons" to "make sure that our conventional weapons capability is an effective deterrent in all but the most extreme circumstances."
The Times suggests that Obama is prepared to give countries that adhere to the NPT the benefit of the doubt even if they use chemical or biological weapons to attack the United States and its allies, including NPT-signers like China and Russia.
This policy would be subject to revision if other countries advanced their capabilities in such a way that would significantly increase the threat to the U.S. and its allies.