Editor's note: William Tobey is a senior fellow at Harvard University's Belfer Center for Science and International Affairs. He served on the National Security Council staff under three presidents.
(CNN) -- Presidents are extremely reluctant to limit their freedom to act before circumstances force them to make choices. "I'm not going to answer hypothetical questions" is often heard from the presidential podium.
Why then would President Obama seemingly limit his own options to defend American security by accepting limits on employment of U.S. forces in his newly released Nuclear Posture Review? The answer is he has not, because, in reality, not much has changed.
But one area where the 2010 Nuclear Posture Review might have a meaningful effect -- and a deleterious one -- is in improving the safety, security, and reliability of our nuclear stockpile. The new policy states flatly, "The United States will not develop new nuclear warheads." It anticipates programs to extend the life of existing warheads, but that work will not include new designs.
The U.S. nuclear arsenal is aging. The newest weapon was deployed two decades ago and others are much older.
Since then, technologies for making nuclear weapons safe from accidental detonation and secure from unauthorized use have improved, even as the threat posed by nuclear terrorism has grown.
Indeed, the 2010 Posture Review cites nuclear terrorism as the foremost threat we face. We now require and can design greater margins for safety and security. Refusing even to consider designs that might respond to these developments is breathtakingly Luddite. The tools of science are fundamental to nuclear safety and security; ruling out new designs is the triumph of ideology over science.
The other aspects of the strategy will not have such a big impact. For example, Obama's policy pledge that the United States will not use nuclear weapons even in retaliation for a chemical or biological weapons strike looks, on the surface, like a departure from previous policy.
By the way, this is not a completely hypothetical issue. Before the first Gulf War, then-Secretary of State James Baker successfully employed a policy of "calculated ambiguity" about a possible U.S. nuclear response to Iraqi chemical or biological weapons attacks. The first Bush administration had determined it would not respond with nuclear weapons, but wanted to do everything possible to deter such attacks in the first place.
But Obama's administration has introduced its own "calculated ambiguity," hedging its commitment by stating, "The United States reserves the right to make any adjustment in the assurance that may be warranted by the evolution and proliferation of the biological weapons threat and U.S. capacities to counter that threat." In other words, the pledge is good until circumstances change.
What about the administration's related pledge not to use or to threaten to use nuclear forces against non-nuclear weapon states that are in compliance with the Nonproliferation Treaty? The exceptions to the pledge, aside from certain of our allies, would include Russia and China, which are nuclear weapons states, and North Korea, Iran, and Syria, which have violated the Non-Proliferation Treaty or its associated Safeguards Agreements. North Korea has also withdrawn from the treaty. Thus, there has been little, if any, narrowing of contingencies potentially to be dealt with by U.S. forces.
For the most part, the 2010 Nuclear Posture Review incrementally advances policy in response to trends in evidence since the end of the Cold War. The United States has greatly reduced its nuclear arsenal and reliance on nuclear weapons to deter aggression. Indeed, the two Presidents Bush combined reduced the U.S. nuclear arsenal significantly -- by my calculation, about 80 percent -- from its level at the end of the Cold War. That is all to the good.
The five key goals of the new policy -- "preventing nuclear proliferation and nuclear terrorism; reducing the role of U.S. nuclear weapons in U.S. national security strategy; maintaining strategic deterrence and stability at reduced nuclear force levels; strengthening regional deterrence and reassuring U.S. allies and partners; and sustaining a safe, secure, and effective nuclear arsenal" -- were all held by earlier administrations.
But so long as nuclear weapons exist, we will require a safe, secure, and reliable nuclear deterrent. That can only be guaranteed by a willingness to apply our best scientific resources to the task. To do otherwise is to handicap ourselves to the detriment of national security.
The opinions expressed in this commentary are solely those of William Tobey.