Nuclear Chain Reaction
The US shock-and-awe campaign to rebalance burdens among its partners has been running for less than two months but allies’ anxieties about American security commitments have already spilled over into the nuclear domain. On February 24, after questioning whether NATO would remain in its current form given US retrenchment, Germany’s presumptive chancellor, Friedrich Merz, called for talks with France and the United Kingdom about extending their nuclear protection. Shortly afterwards, French President Emmanuel Macron agreed to open “the strategic debate on the protection of our allies on the European continent through our (nuclear) deterrence”.
Merz elaborated his position in early March. “The sharing of nuclear weapons is an issue we need to talk about. … We have to be stronger together in nuclear deterrence. … We should talk with both countries [France and the United Kingdom] always, and in addition, from the perspective of supplementing the American nuclear shield, which we of course want to see maintained,” he said.
Assumptions drive some of this anxiety more than declared US policy. Senior Trump administration figures have been careful to qualify provocations with reaffirmations of “core” US alliance commitments. These presumably include extended deterrence. But the allied reaction should not be dismissed as a reflexive response to sudden American policy shifts. US partners will recall, without fondness, candidate Trump’s alarming statements in 2016 that linked Washington’s NATO Article 5 obligations to allies’ defense spending. He also suggested that some of them should pursue their own sovereign nuclear deterrents.
The first Trump administration’s 2018 Nuclear Posture Review (NPR) ultimately reassured US allies. That document displayed a remarkable level of continuity and reaffirmed long-standing American security commitments. The policy, however, was the product of a balance of power between Congress and the administration that guided the outcome toward continuity. That is not where Washington seems to be now, and allies are probably wise to judge that Trump’s views have not moderated as much as the 2018 NPR implied.
The threat environment has also shifted materially over the past six years. Russia has revived Cold War-era posturing and, through its nuclear coercion of Ukraine, steamrolled over international norms and laws prohibiting threats against a non-nuclear state. China has accelerated its nuclear buildup, and North Korea and Iran have extended their contraventions of UN Security Council resolutions. Progress on disarmament has stalled. It is clearly a bad time for uncertainties about the reliability of the US nuclear umbrella.
Notwithstanding Europe’s determination to shore up its own deterrence capabilities, there are fundamental limitations to the role that existing European nuclear states can play, certainly over the medium term. British and French nuclear inventories represent modest complements to the much larger US arsenal. The former is exclusively submarine-based, dependent on US Trident missile delivery systems and subject to stringent US controls. Moreover, UK nuclear forces are already integrated into NATO’s nuclear framework. France’s nuclear deterrent is more independent and multidimensional, comprising air and submarine platforms, but it is designed to meet the country’s sovereign needs, not the broader alliance’s. Both countries would need new and expanded systems if they were to increase their contributions.
In this respect, France and the United Kingdom collaborate bilaterally on nuclear weapons technology under the 2010 Teutates Treaty, and France has expanded its weapons facility at Valduc. But it would be difficult for either country to fill a deterrence gap independently of the United States. Seeking to do so would almost certainly provoke a Russian response and unleash strong criticism from nuclear disarmament advocates. Permanently stationing French nuclear weapons elsewhere in Europe would be problematic under the Non-Proliferation Treaty (NPT) (Russia was rightly criticized for placing weapons in Belarus.) France could rotate nuclear-capable aircraft through allied airbases, perhaps on a “neither-confirm-nor-deny” basis, though this would still likely prompt a Russian response while providing only a small deterrence benefit.
No such options exist for US allies in the Indo-Pacific, which remain wholly dependent on the American umbrella. When, on March 7, Trump expressed disquiet (and a disregard for Japan’s security policy evolution) at a perceived imbalance in the US-Japan security relationship (“… we have to protect them, they don’t have to protect us.”), Japan’s chief cabinet secretary, Yoshimasa Hayashi, quickly sought to reassure the American and the Japanese publics. Hayashi emphasized the potential for limited exercise of the right of collective self-defense, introduced through legislative change in 2015, and expressed confidence that the United States “will fulfill its obligations stipulated in the treaty, using all types of capabilities, including nuclear weapons”.
No non-nuclear US ally has yet indicated an interest in contemplating its own nuclear deterrent in response to the current security policy upheaval. But, given the limited options available within existing frameworks, this is a risk that should not be ignored. Several US allies and partners already hedge with latent nuclear deterrence, whereby states possess dual-use nuclear technology under NPT provisions. Japanese Prime Minister Shigeru Ishiba referred explicitly to this “tacit nuclear deterrent” in 2011, stating that “I don’t think Japan needs to possess nuclear weapons, but it’s important to maintain our commercial reactors because it would allow us to produce a nuclear warhead in a short amount of time.”
Nobel laureate Thomas Schelling observed in 1976 that a country’s nuclear-weapon status should not be described with a “yes” or a “no” but rather with a time schedule. In this context, pathways that seemed unthinkable just a short time ago are not insurmountable for technically capable nations with existing nuclear industries and advanced militaries. Several US allies could move rapidly to acquire the essential components (fissile material, delivery systems, and miniaturized nuclear warheads) if they chose to do so, although they would likely need to conduct testing to demonstrate effectiveness, breaching further international obligations.
Any move toward serious exploration of a sovereign nuclear capability by a non-nuclear US ally would seriously undermine, if not destroy, the NPT and the architecture that supports it (arguably the most significant security achievement of the post-World War II international system). None of the P5 would want this, nor would most parties to the treaty.
For the United States, there is no clearer demonstration of the disadvantages of an uncompromising America-first foreign policy than this scenario. But even without it, emerging region-centric discussions on deterrence will naturally diminish American influence.
Washington, ideally starting with the president, needs to be more explicit in its deterrence messaging to settle allies’ and other partners’ nerves. Trump himself has indicated he wants a debate about nuclear policy and disarmament, although he is seemingly motivated substantially by fiscal considerations.
Stabilization is not just a US responsibility. European and Indo-Pacific allies need to engage Washington about the future of deterrence under rebalanced security arrangements. Such engagement could eventually be folded into a refreshed NPR process (although the last iteration was released in 2022, the strategic context has clearly shifted since then). On the European side, French participation in NATO’s Nuclear Planning Group would have demonstrative and practical coordination benefits. It is also crucial for US allies to shape public debate and understanding about the importance of nuclear deterrence to national, regional, and global security. And allies should prioritize conventional capabilities that could contribute to tactical deterrence.
As governments consider their next steps, one of their overriding considerations should be the contribution that clear and consistent policy messaging itself makes to deterrence. There is currently a danger of strategic policy turbulence doing the opposite.