At a meeting earlier this year, top foreign ministry officials from several European countries were asked who among them still believed that the United States would come to their defense if they were attacked. Not a single hand went up. It was a stark indication of the extent to which European governments have concluded that the United States—for so long the backbone of European and NATO security—is no longer a reliable ally. Over the past 18 months, conversations in Brussels and in other NATO capitals have revolved around how to boost the continent’s conventional defense to make up for Washington’s retrenchment. But a quieter and more urgent discussion is also taking place, focused on the status of the ultimate deterrent: the U.S. nuclear guarantee.

More than half a century ago, the Great Debate, as the French strategist Raymond Aron termed it, broke out between European countries and the United States over how to preserve European nuclear deterrence in the face of the Soviet Union’s expanding nuclear capabilities. Then, European leaders feared that Washington’s growing emphasis on the conventional defense of the continent reflected an increasing reluctance to protect Europe with nuclear weapons—especially as Moscow developed missiles that could reach the U.S. homeland.

Would the United States be willing to risk Boston to defend Berlin? That debate was ultimately resolved through a new grand bargain: in return for a commitment from European countries to forgo developing nuclear weapons, the United States would invite more European participation in nuclear decision-making. That essential bargain stuck for 60 years, helping secure both the United States and Europe and preventing nuclear proliferation.

Now, however, that bargain has come undone. Washington says that it wants a new division of labor: the Europeans need to take on primary responsibility for their conventional defense while the United States continues to ensure their nuclear defense. But that hardly addresses the problem. “If you don’t believe in the United States’ Article 5 commitment,” one of the officials attending the meeting told me, “then extended deterrence is effectively dead.”Already, alternative options are being considered. In some European capitals, officials are quietly raising the possibility of acquiring their own nuclear weapons. France, meanwhile, has offered to adapt its nuclear policy to help defend its European allies.

Each of these options has real logic. But none of them adequately addresses the problem of ensuring European security without risking further proliferation. A better approach would be a fourth alternative: a renewed U.S.-European nuclear bargain, this time with a real European core. Led by France and the United Kingdom, NATO’s European members need to take on a larger role in their nuclear deterrence while working to restore the transatlantic defense link that has been the foundation of U.S. and European security for so many decades.

FOUNDATION OF PEACE The Soviet Union’s 1957 launch of the Sputnik satellite posed a profound dilemma for NATO. Until then, the alliance had counted on U.S. nuclear weapons deployed in Europe to deter an attack by a much larger Soviet conventional force. But once Moscow demonstrated its ability to launch intercontinental rockets, Europeans feared that the United States would no longer be willing to use nuclear weapons to prevent a Soviet invasion of Europe.

These concerns prompted a fierce debate within NATO about how the continent could ensure its nuclear defense. Some, led by France, were convinced that European countries needed their own nuclear weapons. Others sought less costly ways to restore some control over nuclear deterrence. One American idea that gained substantial traction was to create a so-called multilateral force—a fleet of vessels carrying some 200 missiles. Such a multilaterally operated and funded force could give Europeans a sense of ownership and control over the use of nuclear weapons, the thinking went, while preserving the U.S. president’s final authority over their launch.

The debate exposed a fundamental problem with extending U.S. nuclear deterrence to allies, especially if an ocean separates those allies from Washington. An adversary might be deterred from attacking an American ally by even the small possibility of a U.S. nuclear retaliation; the consequences of a miscalculation would be catastrophic. But that same small possibility would offer little comfort to the ally, who needs to believe that Washington would actually risk nuclear devastation on its behalf.

Denis Healey, the United Kingdom’s defense secretary throughout much of the 1960s, postulated what became known as the Healey theorem: “It takes only a five percent credibility of American retaliation to deter an attack, but it takes a 95 percent credibility to reassure the allies.”The Sputnik launch posed a profound dilemma for NATO.

The debate was ultimately resolved through a bargain. Washington’s European allies agreed to forgo their right to acquire nuclear weapons in return for a greater say in U.S. nuclear weapons policy and strategy. Although the idea of a costly multilateral force was abandoned, the creation of the NATO Nuclear Planning Group (NPG) provided a vehicle for Europeans to give input into U.S. nuclear planning and for Washington to demonstrate that European security interests were integral to its nuclear strategy and force posture. Reassured, European countries (aside from France and the United Kingdom) agreed to codify their nonnuclear status in the 1968 Nuclear Nonproliferation Treaty.

Many European countries retained ground- and air-based systems that could deliver U.S. nuclear weapons deployed on their territory. Today, about half a dozen European countries still deploy dual-capable aircraft that can carry U.S. B-61 nuclear bombs. These nuclear consulting and sharing arrangements proved far more crucial to reassuring allies than the hard-power measures (such as counterforce targeting, low-yield weapons, and greater precision) that U.S. strategists typically believe were essential. The latter measures focused on resolving the five-percent problem; the former addressed the 95-percent questions.

France was the only country to reject this nuclear bargain. (The United Kingdom had become a nuclear power in the 1950s, but it committed all its weapons to NATO and participated in the NPG and the dual-capable aircraft missions.) Under President Charles de Gaulle, France came to believe that it could not count on another country for its nuclear security. Paris embarked on its own nuclear program, refused to participate in the NPG or the dual-capable aircraft mission, and, in 1966, withdrew from NATO’s military command structure. The overall bargain, however, laid the foundation for what has become a highly successful deterrence, reassurance, and nonproliferation regime.

DEAL BREAKER Unlike in the 1960s, today’s nuclear debate has not been prompted by a change in the global balance of power. It has been precipitated by a unilateral change in the United States’ attitude toward Europe. As I explained in last year, in Trump’s second term, the United States has rejected the two core principles of NATO’s collective defense commitments: that there is a shared understanding of the threat to NATO members and that members’ security is indivisible.

European members of NATO can no longer assume that the U.S. commitment to their security—derived from the fundamental idea, born of two devastating world wars, that American security is inextricably linked to the security of Europe—is ironclad. Instead, as the Pentagon’s policy chief, Elbridge Colby, has repeatedly noted, “under President Trump’s leadership, the simple fact is that countries can no longer take America for granted.”

European countries have never taken America for granted. They have assumed that it shares their belief in the indivisibility of U.S. and European security—and they proved their own commitment to this belief when NATO invoked Article 5’s collective-defense obligation for the first and only time, in response to the September 11, 2001, attacks on the United States.

The American president and other senior officials have made it clear that the United States’ security commitment to Europe is based not on a shared understanding of the threat that both entities face but on secondary considerations, such as European countries’ level of defense spending and their support for U.S. foreign policy. In August, the Pentagon sent its 31 NATO allies a long questionnaire stressing the conditionality of Washington’s security commitment: it asked them to profess their loyalty to Trump’s foreign policy, commit to procuring defense equipment from U.S. firms, and prioritize funding the restoration of the U.S. industrial base by opposing any “buy European” initiatives.

Some European NATO leaders still refuse to admit in public that anything fundamental has changed. Privately, though, most have reached the same conclusion as senior European political officials: that the United States can no longer be counted on to come to Europe’s defense. And if that is true when it comes to conventional defense, it is even more true with respect to the nuclear guarantee. That leaves Europe facing questions it has never had to ask before. What if Russia attacked NATO territory and Washington told Europe it was on its own?

How would nonnuclear allies stand up to a nuclear-armed Russia? What if Moscow used nuclear threats, implicit or explicit, to try to force Europe to end its support for Ukraine? None of these scenarios are far fetched. Russia has issued veiled nuclear threats against Europe repeatedly since 2022, most recently in September, after NATO conducted air exercises above northeastern Poland, near Kaliningrad.

FOOL’S BARGAINS Three options have begun to emerge to fill the gap created by the change in U.S. policy. Washington favors reestablishing the nuclear bargain with a new distribution of responsibilities, which it calls NATO 3.0. “We will continue to provide the U.S. extended nuclear deterrent,” Colby told NATO defense ministers earlier this year, “with Europe taking the lead for its conventional defense.”The United States has even suggested that it might be willing to expand its nuclear umbrella by extending its nuclear sharing arrangements to other countries (Poland, for instance) and developing a next-generation nuclear bomb for potential deployment in Europe.

But this option ignores the core problem. The Trump administration has done nothing to convince its allies that the United States remains committed to NATO other than saying so. No additional weapons deployments can compensate for the central implication that U.S. security commitments to European allies are now conditional on political loyalty.

A second option would end the nuclear bargain altogether. In its place, European countries would acquire their own nuclear weapons. The clearest statement of this idea came in March 2025, when Polish Prime Minister Donald Tusk told the country’s parliament that “we would be safer if we had our own nuclear arsenal, that is beyond doubt.”A year later, he told his cabinet that Poland would “strive to prepare . . . for the most autonomous actions possible” on nuclear security.

And Poland isn’t the only country thinking seriously about this option. In Sweden, some politicians have invoked the country’s secret nuclear program during the 1960s to indicate their interest in pursuing a national option. Even in Germany, where discussions of defense have historically been constrained by its own history, a Bundeswehr general argued publicly earlier this year that Germany “needs its own tactical nuclear weapons,” an assertion that would have been unthinkable just a few years ago.

Similar ideas are being voiced in Asia, especially in South Korea, raising the prospect of a cascade of allied proliferation. U.S. security commitments to Europe are now conditional on political loyalty.

In theory, if more European countries acquired nuclear weapons, it could resolve the extended deterrence dilemma. In practice, it isn’t a workable solution. It would take many years for Poland, Sweden, or even Germany to develop independent nuclear deterrents. European nuclearization would break the Nonproliferation Treaty architecture that the original 1960s U.S.-European nuclear bargain was built to protect, and it could set off a nuclear arms race that could make Europe less, not more, secure. A strategy designed to bolster deterrence would end up weakening the very alliance structure it aimed to strengthen.

As an alternative to these two options, France has spearheaded a third approach that would aim to replace, or at least augment, the U.S. umbrella. French President Emmanuel Macron proposed this solution in a speech in March 2026, announcing a “forward deterrence” initiative that would include European allies in nuclear training exercises, temporarily forward-deploy French nuclear-capable aircraft on allied soil, and host extensive nuclear discussions with participating countries. So far, ten European countries have joined the initiative by establishing bilateral nuclear steering groups to discuss French nuclear strategy and how its evolution could enhance their security.

The Macron proposal represents a major evolution in French thinking by explicitly extending France’s vital interests to include the security of its European partners. Paris’s willingness to engage European neighbors in direct talks about nuclear issues is welcome. But there are real drawbacks to such an initiative. In his announcement, Macron reiterated the long-standing “four nos” that underpin France’s defense doctrine: no joint decisions on nuclear use, no joint nuclear planning, no shared definition of French vital interests, and no nuclear guarantee “in the strict sense of the term.”The framework’s reliance on bilateral discussions also weakens the idea that Europe’s defense ought to be a collective NATO effort.

And crucially, France’s nuclear doctrine—which allows for a warning shot, followed by a devastating response if the warning fails to deter the adversary—gives it fewer options for managing conflict than does NATO’s more flexible strategy, which allows for gradual escalation. This narrower range of options could make its nuclear threats less credible in a conflict over an ally’s security. In the end, the French proposal would add a measure of reassurance and deterrence, but not enough to overcome the voids created by the change in U.S. policy.

MUTUALLY ASSURED PROTECTION None of the three options now being discussed resolve Europe’s extended nuclear deterrence dilemma. But elements of all three point to a possible solution. NATO needs to bolster both the European and the U.S. legs of its nuclear deterrence posture, bring France into its nuclear consultation and planning structures, and extend the existing nuclear sharing arrangements to incorporate additional members. These tasks will require NATO members, especially its three nuclear powers, to make significant adjustments to their existing beliefs and policies. The alternative is not the status quo—which is already unsustainable, given the nature of the Russian threat and the changes in U.S. policy—but rapid nuclear proliferation.

NATO countries will need to agree to three major adjustments in their nuclear posture: in the number and kind of weapons deployed, in how nuclear and nonnuclear NATO members consult one another, and in the alliance’s doctrine for using nuclear weapons. First, NATO nuclear powers need to modernize their nuclear forces. The United States should replace the B-61 gravity bomb, which will be difficult to use effectively against heavily defended targets, with a stand-off missile that can reach deep into Russian territory from NATO airspace.

Such a modernization is long overdue. In addition, European nations should agree to develop a long-range missile that could be outfitted with a nuclear warhead developed jointly by France and the United Kingdom. The missile should be financed by European countries and be deployable on aircraft owned and operated by nonnuclear allies. Finally, these new U.S. and European nuclear capabilities need to be based in a wider range of NATO countries, expanding European participation in the nuclear deterrent mission.

Changes to hardware are necessary to restore the credibility of Europe’s nuclear deterrence. But the software of consultation needs to be at the core of the effort, as it was in the 1960s. Back then, France refused to join the NATO consensus and withdrew from the integrated military command structure. Even when it returned, in 2009, its nuclear deterrent remained fully independent, and it did not join the Nuclear Planning Group. That insistence on independence is what led Paris to pursue bilateral nuclear arrangements this year.

But these parallel bilateral discussions not only create confusion and distrust about Paris’s true intentions among dialogue partners; they also fail to foster the cohesion that could come from a collective European nuclear deterrence dialogue. The security of Europe and the United States is, in fact, indivisible.

Put simply, Paris needs to join the NPG. Doing so would not automatically place its nuclear capabilities under NATO command and control. But it would give European partners a better understanding of French thinking and afford France more knowledge of European requirements for deterrence and reassurance. European NPG members could agree to meet regularly without the United States to discuss how to integrate the new European nuclear missile forces into NATO’s nuclear strategy. For many years, countries hosting U.S. nuclear forces have met separately from other NATO members in the NPG; a similar, European-only caucus would build on that precedent.

The third necessary adjustment needs to be doctrinal. One element of NATO’s nuclear doctrine cannot change: that the ultimate decision to use nuclear weapons will always reside with the nuclear powers, France, the United Kingdom, and the United States. These decisions cannot be delegated. And national nuclear deterrents will continue to be guided by national doctrine, not subject to NATO control. If France wants to retain its one-warning-shot escalatory doctrine, it can do so, even after it joins the NPG.

But it would need to explain how this doctrine would reassure allies and enhance deterrence. At the same time, France’s participation in the NPG and the addition of the new European nuclear missile force would expand Europe’s influence over the development of NATO nuclear strategy. And it would confront Moscow with the reality that the decision to use nuclear weapons in Europe’s defense no longer rests in Washington’s hands alone.

These are major posture adjustments that will require significant changes in policy and perspective. Washington will have to accept that the deployment of additional European nuclear forces means it can no longer dictate NATO’s nuclear policy and strategy—including, ultimately, the decision to use nuclear weapons. Paris, meanwhile, must accept more integration into NATO. London will need to extend its nuclear cooperation with the United States to France, develop a second nuclear system (in addition to its submarine force), and find the resources necessary to design and build a new warhead in collaboration with France.

Nonnuclear European countries will have to agree to finance the development and procurement of new missile systems and possibly airplanes (although not nuclear warheads, which would violate their treaty commitments). They must also collectively finance security, communications, and other upgrades to enable the expanded deployment of dual-capable aircraft. Most important, these nonnuclear allies would need to reiterate their commitment to forgoing nuclear weapons of their own, reaffirming the essential bargain that was cemented 60 years ago.

None of this will happen quickly or easily. It will require London, Paris, and Washington to give up an element of control over their nuclear arsenals that each has jealously guarded for more than 60 years. But the alternatives are worse. The security of Europe and the United States is, in fact, indivisible, no matter what the current administration in Washington may believe. If Europe were left to fend for itself and nuclear weapons spread from capital to capital, Americans would be less safe, not more.

Yet U.S. retrenchment is also real, and no amount of reassurance from Washington will restore the credibility of a nuclear guarantee that Europeans have come to doubt. With the United States pulling back, a new bargain in which Europe carries more of the nuclear burden and has more say in the choice to use these weapons is the only way to ensure transatlantic security.