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Biden’s proposal for a US “sole purpose” nuclear declaratory policy

Consequences for allies in Asia, NATO and Germany

SWP Comment 2021/C 62, 23.12.2021, 8 Seiten



US President Joe Biden is considering a change to US nuclear declaratory policy. Ever since the beginning of the nuclear age, Washington has stated that it could retaliate with a nuclear response to both nuclear and non-nuclear attacks. This declaratory policy may soon be restricted: President Biden would like to reduce the role of nuclear weapons through a “sole purpose” (SP) declaration. Accordingly, the sole purpose of US nuclear weapons would be to deter and, if necessary, respond to nuclear attacks. The United States would pledge to never use nuclear weapons against conventional aggression. However, contrary to the expectations of SP pro­ponents, this change would hardly reduce the nuclear risks that the United States face today. Moreover, US allies in Europe and Asia already fear that SP would diminish their security. For Germany specifically, it is worth asking what kind of political and military consequences an SP policy could have.

In July 2021, the Biden administration launched its Nuclear Posture Review (NPR), an assessment in which every new US admin­istration engages. The process is scheduled to be completed in early 2022. An NPR contains, among other things, the nuclear declaratory policy of the United States. Through these reviews, Washington com­municates to adversaries and allies the poli­tical and strategic aims of the US nuclear arsenal, as well as the military capabilities required to achieve them. In addition, the NPR also explains the conditions in which the United States could use its nuclear weapons. Throughout this process, the Biden administration has been confronted with conflicting priorities – one reason why the current NPR is so hotly debated.

Biden’s competing objectives

On the one hand, the president wants to reduce the role of nuclear weapons within US security policy, as announced by the White House in its “Preliminary Guidance for a National Security Strategy in March 2021. Biden has long argued that a reduced role for nuclear weapons would be desirable and serve US security interests. As early as 2017 (then as vice president) and again during the 2020 election campaign, he proposed a “sole purpose” declaratory policy – although he never spelled out the expected benefits of this policy change.

On the other hand, President Biden has pledged to strengthen US alliances, not at least as a departure from Trump’s policies. Nevertheless, most allies rely on US extend­ed nuclear deterrence. They see their secu­rity as dependent upon Washington’s promise to defend them, even with nuclear weapons if necessary. Since SP threatens to limit this nuclear umbrella, many allies reject such a change to the United States’ declaratory policy.

There is therefore a discrepancy between Biden’s goal of reducing the role of nuclear weapons in US security policy through SP and his aim of strengthening US alliances, which rely upon nuclear reassurance. The tension between these goals could be re­solved if the threat to allies – and thus their need for America’s nuclear protection – was relatively low, in which case the United States could reduce the role of its nuclear arsenal without undermining its alliances. This appears to have been Obama’s logic in 2009, when Russia and NATO, for instance, still maintained a strategic partnership.

Since then, however, the security situation has deteriorated. Several NATO allies, as well as US allies in the Pacific, feel threatened by the extensive military build-ups and aggressive foreign policies of Russia and China. As a result, these allies empha­size the importance of US extended nuclear deterrence for their security. As for the other nuclear-armed states (Russia, the United Kingdom, France, China, Israel, India, Pakistan and North Korea), the role of nuclear weapons is not diminishing either. On the contrary, it is increasing nearly everywhere.

Against this backdrop, Biden’s idea of SP is controversial in Washington. Republican members of Congress strongly criticize the proposal and the US Departments of State and Defense have also voiced concerns. Advocates nevertheless adhere to the idea of SP and emphasize three primary argu­ments.

The expectations of sole purpose proponents

First, advocates hold that SP would increase crisis stability. Currently the United States upholds “strategic ambiguity”, thereby deliberately not ruling out the option of nuclear first use in crises. This approach is based on the calculation that the un­predictability of such a policy strengthens deterrence vis-à-vis other states: if opponents do not know the threshold beyond which the United States could respond with nuclear weapons, they will shy away from pushing the boundary.

SP proponents, however, argue that in the event of a crisis, adversaries fear not only a limited first use, but rather a dis­arming nuclear first strike. In this case, the United States would pre-emptively destroy the opponent’s entire nuclear arsenal in order to dominate the conflict with the help of its remaining nuclear weapons. In order to prevent this outcome, US adversaries could see themselves forced to use their nuclear weapons at an early stage in a crisis, before US missiles destroy their arsenal – the so called “use them or lose them” dilemma. According to its supporters, SP could prevent such escalatory dynamics, as challengers would believe ex ante that the United States would employ nuclear weapons only to deter and, if necessary, to respond to nuclear attacks. The greater predictability of US behavior would encourage opponents not to fire their nuclear weapons in a crisis, and thus nuclear conflict would become less likely.

Secondly, greater transparency in US policy would make the use of nuclear weapons less likely even outside of crisis situations. According to critics of “strategic ambiguity”, the current US policy facilitates misperceptions – such as the misinter­pretation of radar signals – that could ac­ci­dentally trigger a nuclear war. For instance, if erroneous signals suggested that a dis­arming US first strike was underway – and this impression cannot be dismissed, as it does not run counter to US declaratory policy – the false alarm could set into motion a massive nuclear retaliatory strike, triggering an accidental nuclear war.

An SP policy would reduce these risks, proponents argue, for any signs pointing to a completely unexpected first strike by the United States would be seriously ques­tioned. Such a bolt from the blue would contradict the United States’ stated SP policy that it would only use nuclear weapons to deter or respond to nuclear aggressions. Such scrutiny would reveal most mistakes and make accidental escalations less likely.

Third, advocates expect an SP declaration to further the politics of nuclear disarmament. Reducing the importance of US nuclear weapons would emphasize Wash­ington’s commitment to Article 6 of the Non-Proliferation Treaty (NPT), which com­mits all 191 NPT State Parties to “pursue negotiations in good faith on effective measures” to end the nuclear arms race and achieve nuclear disarmament. SP would be a step in this direction and represent a boon from which the upcoming NPT Review Conference in January 2022 could benefit, especially in the face of simmering discontent among many countries over the lack of progress towards disarmament that threatens to derail the Conference. With SP, advocates hope that a positive outcome would be more likely, thereby stabilizing the entirety of the NPT.

Just words, or deeds too

Whether these effects could actually occur depends on how SP would be implemented. In principle, two scenarios are conceivable: 1) a purely declaratory change in US nu­clear policy, and 2) an SP declaration that would be followed by significant changes in the US force posture.

In reality, the desired benefits of SP could only be achieved if the United States fundamentally changed the structure of its nuclear forces. However, such a significant shift in posture is extremely unlikely and the Biden administration will most prob­ably merely adopt a declaratory change, the results of which will likely disappoint SP supporters. The main reason for this: ad­versarial governments give little credence to the words of a US president. For instance, Moscow and Beijing have already voiced their doubts about the seriousness of a US SP declaratory policy.

For US adversaries to believe that the United States sees nuclear weapons only as means for dealing with nuclear aggression, Washington would have to significantly scale back its ability to use nuclear weapons in other situations. The United States would need to credibly signal that it has given up key military options that it could otherwise use to significantly limit an adversary’s retaliatory capability. Just eliminating indi­vidual categories of nuclear weapons, for example, land-based intercontinental ballis­tic missiles (ICBMs), would be insufficient. Even if the United States gave up all its ICBMs, US adversaries would fear that Wash­ington could still launch a first strike in a crisis, or at least have military incentives to use nuclear weapons first. This fear would continue to be buttressed by the large number of US submarine-launched ballistic missiles, by missile defense capabilities and by conventional precision strike capa­bilities. As a result, US adversaries would almost certainly prepare for this worst-case scenario rather than trust Washington’s words alone.

Thus, to convince adversaries that the United States will never be the first to use nuclear weapons, Washington would have to relinquish key strategic capabilities – nuclear and non-nuclear alike – and ulti­mately the US military’s global preeminence. Nothing, however, suggests that this is intended. For US opponents, Biden’s SP would therefore likely be nothing more than empty words of little strategic conse­quence.

Little would change for the United States ...

If Russia and China regard a US SP declara­tory policy as untrustworthy, the policy will not reduce the risks of nuclear escalation in crises or of accidental nuclear use. Since Moscow and Beijing would still be unable to rule out a US first strike, the danger of escalating crises as well as erroneous nuclear use would continue to exist.

It is also unclear why a purely declara­tory SP would deliver decisive advantages within the NPT regime and at the 2022 Review Conference. Disarmament supporters are likely to welcome an SP declaration but criticize the absence of changes in the US nuclear arsenal. Historical experience gives no reason to expect that such a purely declaratory SP could significantly alter the course of the Conference. But even if SP contributed to an agreement on a final docu­ment at the Review Conference, it remains questionable whether there is a link be­tween the outcome of review conferences and the stability of the NPT. There is little evidence that non-nuclear-weapon states will withdraw from the NPT and seek nuclear weapons if nuclear disarmament stagnates.

But if Moscow and Beijing do not find a US SP policy credible, it would also invali­date the assertion that an SP declaration would undermine US nuclear deterrence of massive non-nuclear aggressions. If Russia and China focus on capabilities rather than words, Washington could continue to rely on its nuclear capability to deter conventional war even after an SP declaration.

This discussion does not imply that deterrence built upon “strategic ambiguity” – which would de facto persist in the case of a not-credible SP – is without risks. Any nuclear policy involving a first use option carries increased risk of “inadvertent esca­lation”. By trying to assess the US nuclear threshold, adversaries may miscalculate and inadvertently cross a red line. More­over, so long as nuclear weapons exist, acci­dents cannot be ruled out. These risks are real, albeit extremely small in the case of the United States. However, a purely de­claratory SP does not eliminate such risks.

With regard to the desired positive effects, SP would thus remain almost with­out consequences for the United States. US deterrence options would also hardly change. Politically, however, the costs of SP would be higher, with potential negative impacts on the United States, on Europe and on the US-led international order.

... but much could change for US allies in Asia

As a result of China’s military build-up, the conventional US-Chinese balance of power in the Indo-Pacific has been altered. The Pentagon can no longer be sure that the US would win a limited war with China in which nuclear weapons played no role. Consequently, the superior US nuclear ar­senal is of vital importance. It allows the United States to ultimately retain the upper hand in a military confrontation with China. Therefore, the United States can effectively deter Beijing from starting a major war in the first place.

A purely declaratory SP would not affect Washington’s ability to deter China from conventional aggression because Beijing would distrust the US declaration. It is, however, conceivable that even a purely declaratory change would have an effect on US allies in Asia, who perceive China as a threat. With SP, allies would probably doubt the political will of the United States to stand up for them. In terms of declaratory policy, Washington – albeit no longer able to deter China by conventional means alone – would rather accept conventional defeat than engage in nuclear escalation. Thus, given China’s military superiority at the theater level, Washington’s policy change would appear to leave US allies at Beijing’s mercy. As a result, pressure would likely increase in these countries to either seek political settlements with Beijing or to build up their own (potentially nuclear) deterrent capabilities.

Europe would also be affected, but differently

Consequences in Europe could be similarly destabilizing. During the Cold War, the conventional balance of power in Europe was even worse for US allies than it is today in Asia. The West believed it could deter the Soviet army only with nuclear means. Consequently, for many years, nuclear weapons were indispensable in NATO strat­egy. Today, Europeans still depend on the United States’ military capabilities, even if the conventional balance of power has shifted. Currently, NATO’s overall capabilities surpass those of Russia (although the opposite is true in regional contexts and in certain conflict scenarios). For the proponents of Biden’s SP proposal, this opens the way for a US policy change.

Nonetheless, Europe’s relative impor­tance within US global strategy has also diminished. Washington’s strategic focus has shifted to Asia and to its rivalry with China. These changing priorities fuel doubts as to whether the United States has the will to enter into military conflict with Russia to preserve European security.

In addition, the potential political or military concessions that would be at stake in plausible conflict scenarios in Europe are less important in terms of power politics today than they were during the Cold War. Back then, the European balance of power could have tipped if the Western alliance had lost the Federal Republic of Germany. Today, by contrast, such losses, for example in Eastern Europe, would challenge NATO in its core task, but – it is feared – would be less relevant for global US interests.

From the perspective of European allies, therefore, the question today is not so much whether the alliance has the capabilities to win a non-nuclear conflict with Russia – because it indeed does. Rather, there are doubts as to whether the United States – who is the provider of the critical military capabilities – has the will to provide them.

This question is crucial because in the event of Russian aggression, the conventional forces that NATO currently stations in potential conflict areas (such as in the Baltic or the Black Sea region) would be inferior to the Russian forces on the ground. For NATO to bring its overall strength to bear, the alliance (and, to a large extent, the United States) would first have to deploy additional forces to the conflict area. This would take several days or even weeks. Hence, Russia could hope for a rapid mili­tary success (i.e. “fait accompli”). There are different assessments as to how Washington would react politically and militarily to such a situation, and this is the reason why Biden’s SP plans are so pertinent for Europe.

Difficult questions for NATO-Europe

Like in East Asia, a purely declaratory SP would not weaken Washington’s actual capacity to deter Russian aggression, as Moscow would hardly believe such an SP. Nevertheless, it would create the impression among some allies that the reliability of US security guarantees is declining and that Moscow perceives US assurances as diminished. SP would be a departure from a decades-old policy, as Washington had always – even in much more favorable threat environments – decided that the first use option was a necessary pillar within NATO to deter adversaries from initiating conventional attacks. Now the United States would abandon this policy and declare that its nuclear weapons were merely a means to counter nuclear aggression.

Current debates within NATO already reflect this concern. The two nuclear powers – France and the United Kingdom – as well as many other allies criticize the United States’ SP plans. Especially those states that are geographically close to Russia and at the receiving end of Moscow’s political-military pressure fear that their exposure to Russian blackmail would in­crease in the absence of a reliable US guar­antee. In their view, SP makes conventional wars in Europe once again conceivable.

Therefore, a US decision to adopt SP against the will of its allies is likely to spark controversial debates within NATO. From a political perspective, given the growing number of US-skeptical voices in Europe, SP could be interpreted as further evidence of declining US reliability. From a military perspective, some allies are likely to press for conventional compensation to address the perceived security gap. The likely focus would lie on whether and how conventional means could tackle the reassurance and – in the eyes of Europeans – deterrence gaps that SP created. Allies are likely to call for drastic steps to neutralize Russia’s ability to exert pressure. Specifically, they might call for capabilities to repel Russian aggression on the ground. This would re­quire huge investment, for example, in air and cyber defense. Demands for the deploy­ment of larger NATO units in potential conflict areas are also conceivable. In one study, for instance, the US think tank RAND proposes that 30,000 soldiers be stationed in the Baltic states alone. Recent research underscores that small troop deployments alone do not change an aggressor’s calculus. To reassure local allies, they must be de­ployed as a “tripwire” that prompts re­inforce­ment and could, as a very last resort, even trigger a nuclear strike.

Nevertheless, deterring Russia also requires the ability to inflict damage to Russian territory. Therefore, in order to fill perceived reassurance gaps, it will not be enough to build stronger defensive capa­bilities. To restore the risk to Russia’s terri­tory that SP would reduce, offensive capa­bilities – in cyberspace and the air domain, for example – would also need to be de­ployed or strengthened.

Such steps would require answering difficult questions. Who would provide the troops? NATO’s strategic adaptation launched in 2014 and the subsequent reforms still challenge many allies. Where would the troops be stationed? If on NATO’s Eastern flank, would all allies accept the inherent revocation of the NATO-Russia Founding Act? Finally, who would bear the costs? RAND estimates them at $8 to $14 billion in initial funding for the out­lined defensive capabilities for the Baltic States alone, and at $3 to $5 billion annu­ally thereafter.

These questions relay why, in the short-term, US allies would probably grudgingly accept an uncompensated SP. In the medium and long-term, however, the pressure for military compensation is likely to increase – as is the risk of political fragmentation within the alliance. Moreover, it remains questionable whether conventional substi­tution would actually lead to greater secu­rity. While NATO would deploy capabilities with a defensive intent, conflict parties may find it difficult to distinguish between defensive and offensive conventional deployments. A security dilemma would loom large, and it is uncertain how or if a spiral of rearmament could be averted. Moscow’s threat perception would likely increase, worsening an already difficult relationship.

Moreover, an SP declaration could strengthen the skeptical voices within the current debate on nuclear sharing in NATO. If the significance of nuclear weapons was reduced, some would see it equally neces­sary to revise nuclear sharing arrangements. Furthermore, political-institutional ties could lose importance; if the US govern­ment no longer publicly links its nuclear weapons to conventional scenarios, why should Germany continue to prepare for such scenarios?

These criticisms, however, are based on misconceptions. An SP would not affect the role of tactical nuclear weapons (such as the US gravity bombs stationed in Europe) in NATO strategy, namely their ability to be used in proportional reaction to a limited Russian nuclear first use, and thus deter Russia from such action.

Finally, an SP would lead to disagreement over nuclear strategy among the three NATO nuclear-weapon states. France and the United Kingdom rely on the threat of first use, and therefore reject a US SP. It would further complicate the search for consensus, and lead to a dispute among the three during consultations on NATO’s new Strategic Concept, which is due to be adopted in June 2022.

Berlin is unprepared for the consequences

The potential results of an SP policy must be considered against those interests of Ger­many that have been central to its nuclear policy since the beginning of the Cold War. In addition to the aim of (1) preventing and ending conflict, the Federal Republic sought (2) to ensure that Washington’s security guarantees also entailed risks to US terri­tory, thereby directly incentivising the US to avoid wars confined to Europe. Bonn strove (3) to create an institutional frame­work that allowed it to have a say in the use of nuclear weapons in Europe. It wanted (4) to preserve the US role as guarantor of European security and prevent the US promise of protection from being replaced by a French option. There is much to sug­gest that these interests persist. Therefore, any consequences of SP for NATO would also affect Germany today. Three aspects would be of particular importance in this regard.

First, it remains unclear whether and how new conventional capabilities could close the perceived reassurance gap arising from SP. In view of its economic strength, Germany contributes disproportionally little to NATO’s military capabilities. If the European share of the alliance’s conventio­nal combat power needed to be increased, Germany would be expected to make the greatest contribution compared to other NATO partners. Therefore, if SP were adopt­ed, greater expectations could be placed on Berlin. For Germany’s new coalition government, however, such steps would likely be highly controversial.

Second, a greater German contribution to Europe’s defense would need credible political support from both the ruling government and the Bundestag. Such a contribution could reassure Eastern allies, but finding this support would likely be a challenge for any federal government.

Third, SP could again raise the question of the role of France’s nuclear arsenal in Europe’s security – precisely because Paris would retain the nuclear first use option. During Trump’s presidency, given the palpable doubts about US reliability in many European capitals, France sought to bolster the narrative that Europe needed to strengthen its own capacity to act. In February 2020, President Macron invited European partners to a strategic dialogue on the role of French nuclear deterrence in Europe’s collective security.

However, Paris wants to conduct this dialogue outside of NATO structures, there­by contradicting Germany’s preference to anchor nuclear deterrence issues institutionally within the NATO framework. Berlin is concerned that shifting the debate out­side of NATO would destabilize European security and defense. Moreover, such a shift away from NATO’s nuclear settings could make it politically easier for a future isolationist president in the United States to reduce nuclear security assurances for Europe beyond SP.

Policy Recommendations

Numerous NATO allies – above all France, the United Kingdom and Germany – have made their rejection of a US SP policy un­mistakably clear to the Biden administration in various formats. As long as the decision-making process in Washington has not been completed, they should continue to convey this message. To this end, Germany could pursue a two-fold strategy.

First, bilaterally with Washington, Berlin could continue to seek an intensive diplo­matic dialogue on SP. In doing so, the German government should ask the US administration – and especially the White House and the State Department – to ex­plain the changes in the security environ­ment that justify modifying US declaratory policy and to outline what advantages would arise from an SP declaration, espe­cially in light of the far reaching consequences.

Berlin, for its part, should continue to outline what political and military prob­lems SP would create within the alliance. Eastern and Central European allies would certainly demand conventional substitutions, thus introducing a host of difficult follow-up questions.

In addition, Berlin should explain how SP could damage US nuclear interests in Europe if European support for nuclear sharing were to weaken because of this change. US nuclear weapons were stationed in Europe in order to share the risks asso­ciated with extended nuclear deterrence within the alliance. Moreover, the United States appears to value these nuclear weap­ons as instruments that allow it to signal the will to fundamentally change the course of a limited conflict, and thus deter an opponent. The United States could no longer pursue either of these aims if SP were to call nuclear sharing into question.

Second, Berlin, together with Paris and London, could propose a three-step approach: firstly, all NATO states could publicly declare that conventional capabilities are of paramount importance, but not the only means to deter and, if necessary, terminate non-nuclear aggressions. Secondly, to further reduce nuclear risks, the goal to ensure NATO’s conventional superiority should be reaffirmed so that the threshold for a nuclear first use by the alliance remains as high as possible. These two proposals concern NATO’s conventional defense capabilities.

Thirdly, a new format for consultation could be proposed that includes all allies who see themselves as affected by an SP de­claration. This refers in particular to France, which does not participate in the Nuclear Planning Group or the High Level Group, and Poland, which is not part of the NATO “Quad” (the United States, United Kingdom, France and Germany). This new format would take a long-term, joint approach to the issues that an SP declaration raises for the alliance. The goal should be to foster greater under­standing among allies of the problems that individual countries have with different nuclear postures. It must remain an open question whether consensus can be reached and what conditions would need to be met for SP to be consistent with the security interests of the United States and all allies. In the end, it would already be a success if these consul­tations gradually strengthened allies’ con­fidence in the United States’ political will – not just its military capability – to ensure Europe’s security and defense.

Dr. Liviu Horovitz, Dr. Jonas Schneider and Lydia Wachs are researchers in the International Security Research Division. Dr. Claudia Major is head of the International Security Research Division. This comment appeared within the framework of project STAND (Strategic Threat Analysis and Nuclear (Dis-)Order).

© Stiftung Wissenschaft und Politik, 2021


Stiftung Wissenschaft und Politik

ISSN (Print) 1861-1761

ISSN (Online) 2747-5107

(English version of SWP‑Aktuell 77/2021)