Would France or the United Kingdom be able to replace the United States in providing a nuclear umbrella for Europe? Not really. Let’s consider France, if only because it was Charles de Gaulle who asked that question about US extended deterrence – would the United States trade Boston for Paris? The question, of course, has never been really answered. Now that France stated that its vital interests have a European dimension, it would appear that France is prepared to provide a nuclear umbrella for Europe. But in reality, de Gaulle’s question will return to France: Would France trade Paris for Tallinn? What would be France’s options for stopping Russia’s aggression against a European ally? On the one hand, there is no doubt that the French nuclear arsenal can inflict serious damage on Russia by striking a range of Russian targets, military as well as civilian. Such a threat, in theory, might compel Russia to retreat. However, if we assume that this threat would deter Russia from continuing the aggression, we must conclude that the threat of Russia’s striking the same type of targets in France in response would deter France from threatening a strike to begin with. There is no way to separate these two – if France deters Russia, then Russia deters France.

This problem, of course, appears in the US extended deterrence arrangement as well, but there the calculation is different. The theory is that the threat of a US nuclear involvement is credible because the United States can lean on the full force of its strategic arsenal. In a nutshell, the United States can “hold at risk” enough military targets to ensure that its counterforce strike will “meaningfully limit the damage” to the homeland by weakening the adversary’s capability to retaliate. Furthermore, the idea is that the US will retain undisputed advantage in its ability to inflict damage in subsequent strikes. It is this prospect of eventual victory that is thought to lend credibility to the extended deterrence provided by the United States.

The US theory, of course, has its own problems; one is that it is not known how meaningful the damage limitation would actually be. An adversary can be content with inflicting some damage and may not be concerned that the damage could have been higher had it not been for the US counterforce strike. In the extended deterrence context, one serious issue is that the best way for the United States to limit damage to its homeland is to withdraw from the conflict altogether. These problems notwithstanding, there is at least a somewhat plausible argument that US extended deterrence works.

But it is also clear that it will not work for France or the United Kingdom. Neither country has a reasonable first-strike capability against Russia that would maintain superior damage-inflicting capability at any point of escalation. They could probably count on Russia being deterred from attacking them openly and directly, but there is no credible way they could use a nuclear threat to protect their allies in Europe should Russia attack them.

One might argue that a European nuclear umbrella would introduce enough uncertainty in Russia’s calculations to deter aggression, but uncertainty, like nuclear deterrence, is a double-edged sword. In fact, certainty would serve Europe far better. Had NATO been certain that nuclear weapons could not possibly be used in Europe, it would have had a much stronger hand in helping Ukraine in the war (and indeed avoiding it altogether). Of course, getting to that point would require making sure that Russia cannot use its nuclear weapons. This is difficult but not entirely impossible, and the first step is recognizing that the nuclear umbrella is a problem, not a solution.