Far more non-nuclear states have given up nuclear weapons programs or reversed their intent to develop them than have become nuclear powers, which is the NPT's biggest success. Yet, there are ominous signs that the treaty is unraveling, leading the world to another "tipping point" much like in the 1960s. Israel, India and Pakistan- the only states that didn't ratify the NPT - now possess nuclear arsenals. North Korea withdrew from the treaty and detonated a nuclear device in 2006, using plutonium made by reprocessing spent reactor fuel. Iran continues to enrich uranium, ostensibly for electric power nuclear reactors. But with minor modifications, the enrichment process can be extended to produce weapons-grade material that can be fashioned into a nuclear device.All signatories have "the inalienable right" to research, produce and use nuclear energy for peaceful purposes. They are allowed to enrich uranium and reprocess spent reactor fuel. And with a mere three months notice, any country can withdraw from the treaty if "extraordinary events" have jeopardized its "supreme interests." Between 30 and 40 states have the capacity to "breakout" this way and develop nuclear weapons, warns Mohammed El Baradei, director of the International Atomic Energy Agency (IAEA). Unless present trends reverse, he says, there could soon be more than 25 states with nuclear weapons-many unstable and prone to takeover by extremists.Implementing these new restrictions requires cooperation among the nuclear weapons states and the non-nuclear weapons states - a difficult prospect as non-nuclear states get increasingly fed up with the failure of nuclear states to actually "negotiate in good faith" toward nuclear disarmament. [Barack Obama]'s declaration to seek Global Zero is important for restoring this faith. Nor is his commitment irresponsible. He has pledged that the United States will maintain a credible nuclear deterrent as long as other states possess nuclear weapons.