Believe It or Not: U.S. Nuclear Declaratory Policy and Calculated Ambiguity

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I am told people complain that I am given to drawing fine distinctions. I am. High policy depends upon fine distinctions: and, if people find they cannot understand them, they should entrust their affairs to those who do.

Lord Balfour, U.K. prime minister and foreign secretary


Nuclear weapons are typically seen as the state’s bluntest instruments available, seemingly indiscriminate in their power. Yet nuclear declaratory policy is precision-crafted with each word carefully chosen for its effects on opponents and allies alike. Though he governed in the pre-nuclear age, former U.K. Prime Minister and Foreign Secretary Lord Balfour, to whom these words above are credited, understood the power and complexity of policy. But senior government officials cannot simply craft national policy with “fine distinctions” and let it be. They should express it in both words and deeds so that adversaries and allies will not only receive the message, but understand it and hopefully find it credible.

Words in the age of nuclear weapons have taken on even greater importance as the consequences for misperceptions can change — perhaps even end — civilization. Paradoxically though, clarity is not always preferable. U.S. nuclear strategists have long recognized there is a place for ambiguity in declaratory policy — stating one’s intentions and “red lines” clearly enough to deter attacks, but not so explicitly as to restrict freedom of action or encourage adversary aggression just short of the “red lines.” The current U.S. policy of “calculated ambiguity” states that America will only consider nuclear employment under “extreme circumstances” when its “vital interests,” or those of its allies and partners, are threatened. This leaves it to America’s adversaries to wrestle with whether the United States would consider their actions “extreme” or threatening “vital interests.” Most of the long-running debate on U.S. nuclear declaratory policy centers on the question of the value of this purposeful ambiguity, and in what circumstances it should apply, for deterring attack and assuring allies and partners.



The Obama administration twice reportedly considered adopting a new, more restrictive, nuclear declaratory policy. However, it twice rejected the move as unwise because the security environment had not improved enough and because allies such as Japan, South Korea, the United Kingdom, France, and Germany fiercely objected. More recently, then-candidate for president, Joe Biden, wrote that he wants to revisit this issue at least once more, likely in a forthcoming Nuclear Posture Review. Given the potential consequences of a changed U.S. nuclear declaratory policy — whether it is shifting adversaries’ threat perceptions, alliance dynamics, or domestic weapons procurement — it is well worth exploring whether change is desirable.

America’s current policy of “calculated ambiguity” is worth keeping because it contributes to deterring a growing range of strategic non-nuclear threats (chemical, biological, and conventional), provides U.S. leadership freedom of action in a crisis or conflict, and assures allies and partners. However, influential politicians such as House Armed Services Committee Chairman Adam Smith and Sen. Elizabeth Warren, plus a host of non-government analysts, are proposing changes to U.S. nuclear declaratory policy now because the Biden administration is in the early stages of formulating U.S. nuclear policy. As nuclear modernization programs advance through Congress, the likelihood of restricting or outright eliminating them falls. They hope that if the Biden administration adopts new declaratory policy, that may provide enough impetus to achieve their visions of a reduced U.S. nuclear arsenal. These alternative policies — including nuclear “no first use,” “sole purpose,” and an “existential threat policy” — miss the mark because they seek to restrict U.S. deterrence options through declarations that opponents are unlikely to believe, and allies and partners believe are to their detriment. Instead, U.S. officials should articulate a strong defense of the current nuclear declaratory policy of calculated ambiguity because its flexibility is its strength, and a true necessity in a dynamic security environment.

Calculated Ambiguity: The Deterrent Benefits

The current U.S. policy of calculated ambiguity seeks to signal U.S. intent clearly enough to highlight “red lines,” or situations in which the United States may consider employing nuclear weapons. Yet, it also refrains from telegraphing the type and size of an attack an opponent should expect, should it choose not to be deterred. In essence, it leaves open the possibility of a U.S. nuclear first employment to defend its vital interests, or those of its allies and partners in extreme circumstances. Without using the words “calculated ambiguity,” official U.S. policy states:

The United States would only consider the employment of nuclear weapons in extreme circumstances to defend the vital interests of the United States, its allies, and partners. Extreme circumstances could include significant non-nuclear strategic attacks. Significant non-nuclear strategic attacks include, but are not limited to, attacks on the U.S., allied, or partner civilian population or infrastructure, and attacks on U.S. or allied nuclear forces, their command and control, or warning and attack assessment capabilities.

Except for the sentence identifying what could constitute a strategic non-nuclear attack, the Trump administration’s declaratory formula is essentially a word-for-word copy of the Obama administration’s policy.

Regrettably, U.S. defense officials have rarely discussed publicly the deterrence and assurance benefits of the U.S. policy of calculated ambiguity. When they have, they mostly frame their thoughts by discussing why they would disagree with a possible shift to an alternative policy like nuclear no first use. However, as I discuss in my latest report, there are a number of benefits to retaining a policy of calculated ambiguity.

First, the policy of calculated ambiguity provides a potentially vital deterrent threat before the outbreak of major conflict. By keeping the option open of employing nuclear weapons first, U.S. leaders can make a last-ditch deterrent threat to prevent a major crisis from escalating or a conflict from growing more costly. There is, of course, no guarantee such a threat would work. But alternative policies like sole purpose and nuclear no first use essentially eliminate the possibility of U.S. officials even being able to try in certain dire circumstances. When a crisis or conflict has reached a level of severity where leaders are considering nuclear employment, that is not the time they should be denied what could be their least bad option, threatening nuclear first use to stave off an even worse outcome.

U.S. nuclear declaratory policy requires an adversary to gamble twice. First, they gamble that the United States will not respond to an attack with its nuclear forces, and second, that the attack will achieve its goals in the face of a U.S. conventional response. These gambles, enabled by a policy of calculated ambiguity, can aid deterrence by increasing an adversary’s uncertainty regarding the type and consequences of a U.S. response.

Second, the policy of calculated ambiguity provides U.S. officials with a range of options for crises and conflict that, by their nature, will require U.S. flexibility. They are neither forced to threaten or carry out nuclear first use, nor are they constrained to only consider conventional responses. U.S. officials can keep the threat of nuclear first use implicit or make it more explicit depending on what type of signal they want to send to an adversary. Should they wish to signal their resolve or deter particular behavior, they can clarify U.S. nuclear policy either privately or publicly as the United States did during the Gulf War in 1991 to some effect. Despite the concerns of some like nuclear scholar Scott Sagan, leaving open the possibility of nuclear first use does not commit a U.S. president to employ nuclear weapons first in order to reinforce some vague notion that America keeps its word. When America’s word on the subject of nuclear employment is intentionally vague and non-committal, there is little reason to fear an overriding impulse to unnecessarily employ nuclear weapons. Again, keeping U.S. options open, even extreme ones, during a crisis or conflict allows greater freedom of action to pursue de-escalatory outcomes in addition to providing more chances for nuclear deterrence to “work.”

Third, the current policy of calculated ambiguity allows U.S. officials to consider all options, including nuclear first use, for deterrence in the face of a growing set of non-nuclear threats. The policies of sole purpose or nuclear no-first-use, on the other hand, would (depending on how they are formulated) exclude the possibility of the United States even issuing a nuclear first-use-deterrent threat. Nor would they allow a U.S. nuclear response to strategic non-nuclear attacks on itself, or its allies and partners. U.S. allies and partners, given their geographic location near or neighboring Russia, China, and North Korea, are at the highest risk of suffering large scale chemical or biological attacks — threats that certainly do not appear to be declining.

The United States itself will likely want to at least keep open the option of threatening or employing nuclear weapons first, not only to defend allies and partners, but also to deter or respond to attacks on critical U.S. targets. For example, a Russian conventional cruise missile attack on the U.S. homeland could destroy U.S. nuclear submarines in port (with potentially hundreds of nuclear warheads onboard), disable power plants, or damage terrestrial radars and sensors. Likewise, non-nuclear anti-satellite capabilities Russia and China are developing could target U.S. nuclear command, control, and communications.

Put simply, a U.S. nuclear no-first-use or sole purpose policy, depending on how it is crafted, will not allow the United States to make explicit nuclear threats to deter some of the potentially most-damaging non-nuclear attacks, much less conduct a nuclear response. In effect, these policies could essentially signal, whether intentionally or not, that U.S. policy values withholding even the deterrent threat of nuclear employment over sustaining massive casualties from strategic non-nuclear attack, perhaps up to the point of defeat. Critics may respond that withholding the threat of nuclear employment makes the U.S. commitment to defeating the adversary with conventional means that much more credible. However, like a boxer who ties one of his hands behind his back, it may demonstrate he is committed to only using his other hand, but he will inevitably take a greater beating in the end.

Yes, the United States may eventually win such a contest with its superior conventional forces, but this result is not guaranteed and may come at too high a cost. Given this possibility, why eliminate a valuable deterrent threat, especially when the threat of a U.S. nuclear response can help tip the balance towards preventing a conflict in the first place?

Why Change Policies Now?

Those who wish to make cuts to the U.S. nuclear arsenal see President Biden’s Interim National Security Guidance’s pledge to “take steps to reduce the role of nuclear weapons in our national security strategy” as a golden opportunity to advance their preferred policies. As the Obama administration demonstrated, however, a reduction in the role of nuclear weapons in U.S. national security strategy does not, in fact, require a change in declaratory policy. Rather, the 2010 Nuclear Posture Review cited an improved security environment, increasingly capable conventional weapons, and more regional missile defenses as factors that allowed a reduction in reliance on nuclear weapons, without a significant change to declaratory policy.

Twice the Obama administration reportedly considered replacing current U.S. policy with a sole purpose or nuclear no-first-use policy. Though we do not know the exact formulation officials were considering, it likely would have stated that the sole purpose of the U.S. nuclear arsenal is to deter, and if necessary respond to, nuclear attacks on itself, its allies, or its partners. Then-candidate for president Joe Biden wrote that he supported such a change, but the Obama administration ultimately decided against it, based on a worsening security environment and the objections of allies. Multiple senior Obama administration defense officials remain opposed to adopting such a policy.

Yet there is pressure from the progressive wing of the Democratic Party to pursue bold initiatives that they hope will lead to U.S. nuclear reductions. Thus, Sen. Warren and Rep. Smith introduced a one-sentence bill that would make it the policy of the United States “to not use nuclear weapons first.” Others care less about what the policy is called, whether no-first-use or sole purpose, as long as it results in U.S. nuclear weapons reductions and further restrictions on their employment.

The Biden administration may consider replacing the current policy of calculated ambiguity with one of three different types of alternative policies: sole purpose, no first use, or existential threat.

Sole Purpose: Avoiding the Subject

Advocates of sole purpose or nuclear no-first-use policies acknowledge that, depending on how they are written, they can effectively mean the same thing. For example, Ankit Panda and Vipin Narang acknowledge that Biden’s formulation: “the sole purpose of the U.S. nuclear arsenal should be deterring – and, if necessary, retaliating against – nuclear attack” is substantively the same as a nuclear no-first-use policy. Indeed, other analysts believe they are “equivalent” policies, or different ways of saying the same thing. The Evans-Kawaguchi report even goes so far as to acknowledge that nuclear no-first-use pledges, both past and current, are widely doubted as credible, so states should adopt “a different formulation of essentially the same idea,” that is sole purpose, to avoid being associated with a policy that others have not found credible.

Panda and Narang, on the other hand, prefer a different, more streamlined sole purpose formulation: “The sole purpose of the U.S. nuclear arsenal is to deter nuclear attacks against the United States and its allies.” This phrasing is meant to reassure allies by keeping silent on the issue of “use” (whether first or in response), but they claim there is still room for first use implied within the policy, but it is unclear under what circumstances.

Yet, the United States keeps the option open of employing nuclear weapons first to deter massive conventional, chemical, or biological attacks as well as a number of other strategic non-nuclear attacks. It is precisely these sorts of attacks that allies and partners are greatly worried about, and which U.S. officials could likely not even threaten nuclear employment against for deterrence purposes under their preferred policy. A policy that essentially forbids even threatening nuclear employment in defense of an ally unless it is under imminent threat of attack by nuclear weapons is hardly reassuring. When allies inquire about U.S. nuclear policy, they are not asking U.S. officials to wax eloquent on the purpose of the U.S. nuclear arsenal, they are asking how it would apply in real world situations, (i.e., “use”), exactly the kind of conversation the sole purpose policy is meant to avoid.

Panda and Narang also fail to establish exactly why the United States should switch its nuclear declaratory policy from calculated ambiguity to their version of sole purpose. They rightly acknowledge that adversaries will not believe U.S. statements in either case so there is no benefit there, and given allied pushback on the Obama administration’s attempts to adopt a sole purpose policy there appears to be little benefit in terms of alliances. In fact, they devote only about a sentence-worth of words to the purported benefits of their new policy, saying that it could “meaningfully de-emphasize the role of nuclear weapons in American security strategy” and that it “assures the world — adversaries and allies alike — that the United States would only ever use nuclear weapons in the most extreme of circumstances.” However, current U.S. nuclear declaratory policy already explicitly identifies “extreme circumstances” as the only time the United States would consider employing nuclear weapons. A sole purpose policy’s lack of clear benefits, combined with the likely adverse allied reactions and the growth of strategic non-nuclear threats, makes it both unnecessary and unwise.

No First Use: A More Radical Alternative

While a sole purpose policy actively avoids discussing the possible employment of nuclear weapons, a no-first-use policy opts to emphasize the subject. Ultimately, the end goal is the same: restricting the scenarios in which the United States could threaten to employ, or actually employ, nuclear weapons. But, according to most proponents, like Daryl Kimball, they believe the no-first-use policy’s explicit restrictions are part of its value as a signal to potential adversaries that they need not fear a U.S. preemptive nuclear strike, thus theoretically reducing the possibility of nuclear use in a conflict.

Advocates of nuclear no-first-use (and sole purpose) policies generally articulate six inter-related benefits that the United States might gain from adopting these policies: reduced risk of adversary nuclear first use due to fear of U.S. preemption; a general reduction in bilateral and multilateral tensions; advances in nuclear nonproliferation and perceived commitment to disarmament; foreclosure of an unthinkable and escalatory option; encouragement to keep a conflict at the conventional level; and the creation of the conditions necessary for nuclear weapon reductions whether unilaterally or with others.

To test whether the United States is likely to reap these benefits if it adopted one of these policies, I examined four cases where states adopted a no-first-use policy to see if they benefited in the expected ways: the Soviet nuclear no-first-use policy (1982–1993), the Chinese nuclear no-first-use policy (1964–present), the Indian nuclear no-first-use policy (2003–present), and the Soviet chemical weapon no-first-use policy (1928–present). Remarkably, in each of the cases, the six benefits listed above were almost entirely absent. Simply put, no-first-use policies have a perfect record of failure.

Why? The greatest obstacle to a nuclear no-first-use policy producing the purported benefits for crisis stability or arms race stability is that the other side should believe it, even under the most stressful circumstances. But the examples above indicate that the primary target audience of a state’s no-first-use policy has never believed it fully, whether it was the Soviet Union during the Cold War, or China and India today.

What is even more remarkable is that China and India have, at least until recently, what should be the quintessential nuclear arsenals to project a credible nuclear no-first-use policy. Specifically, they have much smaller nuclear arsenal sizes than Russia and the United States, the weapons are generally de-alerted, and it’s possible that the warheads are separated from the missiles themselves in some systems. If it is possible to create a believable no-first-use policy, then China and India are the ideal test cases. And yet, there is reportedly widespread disbelief among officials and analysts in both countries about each side’s commitment to their respective nuclear no-first-use policies. Recent U.S. defense officials have also claimed they do not believe China’s nuclear no-first-use policy, and the Department of Defense more generally has had long-standing doubts, even before China began its massive current buildup of nuclear weapons.

In short, if a nuclear no-first-use policy does not provide the purported benefits in the best-case scenario, it is even less likely to produce those benefits for the United States.

Existential Threat Policy: The (Somewhat) New Kid on the Block

There exists yet a third camp in the debate over U.S. nuclear declaratory policy that recognizes the potential need to threaten or employ nuclear weapons first to deter or respond to strategic non-nuclear threats, while also signaling a further restriction in the circumstances in which the United States might consider employing nuclear weapons. The “existential threat policy” has the backing of some respected analysts and is worth examining as an alternative to the current policy of calculated ambiguity.

According to George Perkovich and Pranay Vaddi, an existential threat policy would make it U.S. policy to only consider employing nuclear weapons, “when no viable alternative exists to stop an existential attack against the United States, its allies, or partners.” Or, in the words of James Acton:

because of the possibility of escalation, it [the United States] considers that any use of nuclear weapons against itself, its allies, or its partners would constitute an existential threat. But, because existential threats are not limited to nuclear use, this declaratory policy would allow the United States to employ nuclear weapons to defend allies from the most extreme nonnuclear threats.

As its proponents acknowledge, a great deal hangs on the word “existential” and at what point a threat transitions from “severe” to “existential.” Therein, however, lies the weakness of the existential threat policy. For smaller U.S. allies and partners neighboring revisionist powers like China and Russia, even relatively small conventional incursions can be considered “existential threats.” Or, in the example of Seoul, South Korea, massive conventional attacks on the city combined perhaps with chemical and biological weapons use would undoubtedly permanently affect the sovereign political entity of South Korea. But with a potentially sustained and very bloody U.S. response to defend its ally, South Korea could remain a functioning political unit on the world stage. But in those moments when Seoul is under siege and millions of people are fleeing, South Korean and U.S. leaders cannot be absolutely certain that North Korea has war aims that represent an existential threat. Put simply, the United States and its allies may not agree on the severity of an emerging threat during a crisis or conflict and whether it warrants a threat of nuclear first use. But the growing speed and destructiveness of strategic non-nuclear weapons makes an existential threat policy untenable because by the time the United States and an ally agree that a threat has become existential, it may be too late for the threat of U.S. nuclear employment to have the potential deterrent effect.

In addition, an existential threat policy is arguably more vague, detrimentally so, than the current policy of considering nuclear employment only under “extreme circumstances.” Perkovich and Vaddi do not deny that raising the threshold at which the United States would consider employing nuclear weapons may tempt Russia and China to engage in aggression right up to, but not crossing, the “existential threat” line. Their proposed solution is to essentially increase U.S. conventional forces to strengthen deterrence below the nuclear threshold, which the United States is already doing under its current declaratory policy. Thus, it is unclear what net security benefit the United States would gain from adopting an existential threat policy given likely allied reactions and potential adversary responses.

What to Do?

As the Biden administration considers whether the United States should retain the longstanding policy of calculated ambiguity or replace it with some form of sole purpose, no-first-use, or existential threat policies, it should keep in mind that the Obama administration faced much the same situation. It also entered office seeking to reduce the role of nuclear weapons, but found that threats around the world had not diminished in size or severity enough to justify a precedent-breaking change in U.S. nuclear policy. Allies also expressed their opposition to the policy. While it will certainly anger more progressive members of his caucus, though likely not enough to change any votes, Biden should consider following the Obama playbook in two respects.

First, strengthened homeland and regional missile defenses may help reduce U.S. reliance on nuclear weapons by providing supplemental deterrence by denial, lessening the burden on nuclear weapons and their deterrence by threat of punishment. Improved missile defenses can also reduce the risk of inadvertent nuclear escalation by providing U.S. leaders the option of absorbing what appears to be an incoming attack before responding. Second, additional options for long-range precision strike conventional weapons can improve deterrence of regional threats, perhaps lessening the chances of an ally finding itself on the brink of defeat and thus requiring U.S. nuclear threats. These developments may offer an avenue for the Biden administration to achieve its goal of reducing U.S. reliance on nuclear weapons without a change in declaratory policy.

But, potential adversaries also have a vote in just how much nuclear and strategic non-nuclear capabilities grow in salience. The security environment in which the United States and its allies and partners operate is certainly no better, and in some respects much worse, than in 2010 and 2016 when the Obama administration considered and rejected changing nuclear declaratory policy. As Toby Dalton has noted, even after thorough consultations with allies, well-intentioned U.S. nuclear signals can cause adverse allied reactions that make the original action a net loss.

Though the impulse for the Biden administration to differentiate itself from its predecessors will be strong, U.S. nuclear policy should not be the focus for radical breaks from the past. The Obama administration, to its credit, did not confuse its long-term hopes for nuclear disarmament with the short-term reality of rising nuclear and strategic non-nuclear threats, and the subsequent need to modernize the U.S. nuclear arsenal. The Trump administration agreed with the threat characterizations, continued the Obama nuclear modernization program, and did not change U.S. nuclear declaratory policy — it only sought to prudently clarify the policy.

Calculated ambiguity is best positioned among all the other alternative policies to provide U.S. and allied leaders the freedom of action necessary to respond to a growing range of threats. This freedom of action reinforces deterrence against America’s adversaries. Nuclear declaratory policy is far too consequential to become a vehicle for merely signaling U.S. good intentions on nonproliferation and disarmament — a job far more appropriate for U.S. arms control proposals and dialogue. Instead, U.S. officials should clearly articulate why U.S. nuclear declaratory policy is important not only for its deterrence and assurance effects, but also for the range of policy options it can provide that have the best chance of achieving U.S. political and military goals. The tension between when to clarify and when to be ambiguous about U.S. intentions will remain, but preemptively removing the ability to make particular deterrent threats continues to be unwise. The policy of calculated ambiguity may remove the “fine distinctions” that Lord Balfour treasured, but for the purposes of deterring nuclear and non-nuclear threats, it is a “high policy” worth keeping.



Matthew R. Costlow is a senior analyst at the National Institute for Public Policy and the author most recently of A Net Assessment of “No First Use” and “Sole Purpose” Nuclear Policies.

Image: U.S. Air Force (Photo by Staff Sgt. Kevin Iinuma)