To many, the Obama administration's nuclear weapons policy appears to be schizophrenic. In April 2009, in Prague, President Barack Obama pledged to reduce the role of nuclear weapons in U.S. national security policy and to work toward global nuclear disarmament. His aspirations have been reflected in the New Strategic Arms Reduction Treaty with Russia and in a new strategic review, ongoing this summer, that is intended to pave the way for further U.S. nuclear cuts.

But even as the administration cuts the force and talks about a world free of nuclear weapons, it has proposed a major multi-year campaign to replace aging weapons and modernize the U.S. arsenal. The plan calls for a new class of nuclear submarines, new nuclear-capable bomber and fighter aircraft, and updated nuclear bombs, warheads, and missiles. The price tag for this nuclear overhaul is estimated at $185 billion over the coming decade, but the actual cost will no doubt be higher.

Is there a sensible strategy behind these proposals? Does nuclear modernization contribute to deterrence, which the 2010 Nuclear Posture Review called "the fundamental role" of the U.S. nuclear arsenal?

In "The Nukes We Need" (November/December 2009), we described the deterrence challenges that the United States will likely face in the coming years and the nuclear capabilities that might mitigate them. First, we argued that the United States is likely to face tougher deterrence problems in the coming years than it did during the Cold War. Specifically, as nuclear weapons proliferate, it becomes increasingly likely that the United States will find itself in conventional conflicts with nuclear-armed adversaries. Those adversaries have witnessed the catastrophic consequences of losing a war to the United States -- regime change, with prison or death the frequent fate of enemy leaders. Coercive nuclear escalation is one of the only trump cards that countries fighting the United States hold, offering the prospect of a battlefield stalemate and keeping existing regimes in power. For the United States, deterring weak, desperate adversaries from using their nuclear trump card will be a major challenge -- especially as these weapons spread.

Second, we argued that retaining the right mix of capabilities in the U.S. nuclear arsenal is vital for deterring -- or responding to -- an adversary engaging in coercive nuclear escalation. The foundation of a credible deterrent is maintaining the capability and the will to carry out one's threats. But most of the nuclear weapons in the current U.S. arsenal, including all the land- and submarine-based ballistic missiles, have such enormous explosive yields that using them would spread radioactive fallout across vast regions and almost certainly kill large numbers of noncombatants. Threatening to use such indiscriminate weapons would simply not be credible, at least in any scenario short of a nuclear attack on the U.S. homeland. To retain a credible deterrent, the United States must possess nuclear weapons that a president might actually use if U.S. allies, military forces, or territory suffered a nuclear attack. We therefore argued that Washington, as it reduces the size of its nuclear arsenal, must retain and modernize its lowest-yield and most accurate weapons.

So what has happened in the past 18 months? After substantial internal deliberation and input from Congress, the Obama administration has settled on a pragmatic approach to the U.S. nuclear arsenal. That approach balances the administration's two principal goals: reducing the size of the U.S. nuclear arsenal and retaining a robust deterrent for the foreseeable future. Toward the first goal, the administration successfully negotiated and secured the ratification of New START, which caps U.S. and Russian deployed strategic forces at roughly 1,550 warheads -- about 20 percent lower than the previous cap. (All told, the number of deployed U.S. strategic weapons has now been reduced by 85 percent since the end of the Cold War.) The administration is seeking a new round of cuts to further reduce the arsenal.

At the same time, the White House has proposed a major nuclear modernization effort to revitalize the remaining force. Those proposals include funding nuclear infrastructure (that is, the complex of national laboratories, production facilities, and personnel), extending the life of aging warheads, and replacing old delivery systems. Fortunately, the administration's modernization plans seek to preserve the exact capabilities we advocated in "The Nukes We Need."

For example, the administration wants to retain and modernize the lowest-yield nuclear options in the force --the bombs and cruise missiles delivered by aircraft. The White House is seeking funding for a nuclear-capable version of the F-35 Joint Strike Fighter and a nuclear-capable long-range bomber to replace the B-52 and B-2 bombers. Most noteworthy, the administration supports a modernization plan that would convert all remaining B-61 nuclear bombs into a single, low-yield version with increased accuracy. The plan also calls for a new air-launched cruise missile that will probably combine lower weapon yield with higher accuracy.

In addition to preserving the low-yield options in the current force, the modernization plan also calls for building a new generation of ballistic missile submarines to replace the Ohio-class fleet -- a step that is essential for retaining the smaller U.S. arsenal's survivability. There also appear to be plans to increase the accuracy of the missiles that these submarines will carry. If so, the missiles could eventually be armed with much lower-yield warheads than those on current submarines.

All these proposals are welcome since they help ensure that the U.S. nuclear force remains usable -- which is the foundation of a credible deterrent. But there are still reasons for concern. The administration's modernization programs are merely proposals, and they could be derailed. The White House's nuclear weapons policy reflects compromises between competing factions within the administration; those who feel that the modernization plank of Obama's nuclear policy is overshadowing the disarmament plank will likely seek to reopen those decisions if they can. The opportunity to do so might arise this summer, when the Pentagon works on an internal "review of strategic requirements" intended to develop options for shrinking the current nuclear arsenal even further. To that end, the administration will examine potential changes in targeting strategy and alert posture that are still consistent with effective deterrence.

There are additional reasons -- political, economic, and bureaucratic -- to think that U.S. nuclear modernization plans remain vulnerable. Many on the political left remain opposed to modernization, claiming that it will undermine the international nuclear nonproliferation regime. Proponents of nuclear abolition, many arms control analysts, and their allies in Congress have contended that Obama's promise to reduce the role of nuclear weapons in national security strategy is contradicted by his plans to modernize the U.S. force. Those plans, they say, will create new nuclear capabilities and make nuclear weapons more usable.

Among congressional moderates and conservatives, meanwhile, political support for nuclear modernization could erode as lawmakers confront increasingly difficult budgetary tradeoffs. Total defense outlays may drop in the coming years as Washington grapples with long-term budget deficits and mounting debt. Within the defense budget, there will be pressure to prioritize buying weapons that contribute directly to current military operations, such as counterinsurgency and counterterrorism, over the seemingly less urgent task of modernizing the nuclear arsenal.

Moreover, within Washington's bureaucracies, there is little support for nuclear weapons. Those outside the national security community might imagine that the so-called military industrial complex is bent on upgrading the nuclear arsenal, but the reality is far different. The Army and the Marine Corps are out of the nuclear business altogether. And although the Air Force refocused itself on the nuclear mission after recent embarrassing incidents of mishandling warheads and components, its attention is focused much more on stockpile safety and reliability than on nuclear deterrence -- and the military capabilities that support it. In fact, the Air Force has not made a strong public case for retaining the air leg of the nuclear triad, even though that leg is uniquely suited to the flexible, low-yield, high-accuracy requirements of an effective deterrent force.

Defense contractors around Washington, meanwhile, perceive the conventional realm to be more profitable than the nuclear realm. Major aircraft manufacturers, for example, strongly support the procurement of a next generation bomber but have questioned whether it should be made nuclear-capable. Their reluctance is understandable: a non-nuclear capable bomber would be unconstrained by New START, and the Pentagon could buy more of them.

The bottom line is that when it comes to determining a national nuclear weapons policy, at least to this point, the political system has worked. Debates within the administration between the disarmament camp and the deterrence camp, along with input from Congress, have produced a nuclear policy that wisely balances the desire for fewer weapons with the demands of twenty-first-century deterrence.

Only one thing is lacking: an effective campaign to explain this policy to the public. Officials should go beyond the generalities of the term "deterrence" and explain why the United States needs a nuclear arsenal in the coming decades, and why it matters that a deterrent force include usable weapons. That explanation will necessarily require discussing matters that since the Cold War have been mentioned only behind closed doors, such as what types of targets the military might hit and what capabilities it would need to do so. But those are the grim realities of deterrence.

The American public can handle the truth. So can U.S. allies. Explaining how deterrence works, and the logic behind nuclear modernization, will prevent future Congresses from axing programs that have never been adequately explained and lack bureaucratic support yet are essential to U.S. national security.