Author: Derrick Wyatt K.C., Emeritus Professor of Law, University of Oxford. Former adviser to Fide.

The next US Presidential election will be in November 2024. With Trump and Biden neck to neck in the opinion polls, a Trump win seems a distinct possibility. That would place in doubt US support for Ukraine and commitment to NATO, and it could even lead to US withdrawal from the alliance. Either scenario would profoundly affect NATO's European allies. Could they and would they rally round and fill any US defense deficit?

In theory NATO minus America would be left with a viable legal framework for mutual defence, while the EU has its own mutual defense clause. But Europe's problem in defending itself against Russia without US backup is not the wording of legal agreements, but defense capabilities, leadership, and the likelihood or not of European countries being willing to fight to defend each other.

The success of Ukraine's resistance to Russian aggression has shown that a country with a population the size of Spain's can hold its own against Russia's conventional armed forces if it orders mass mobilization and receives enough support from its allies. The USA is the largest provider of military assistance to Ukraine, including vital military intelligence, and weapons like the Patriot missile system which has offered an effective umbrella against Russian air attack.

What the Ukraine experience shows is that while Russia is not invincible, credible resistance to Russia requires well-equipped and well-informed as well as well-motivated armed forces. With assistance from the US and other allies, Ukraine stands at 15 in the 2023 Global Firepower Index, above Spain at 21, and Germany at 25. For comparison, Russia stands at 2 in the same listing, the UK at 5, France at 9, Italy at 10, Turkey at 11, Poland at 20, and Canada at 27. These league placements involve subjective assessments and are far from precise. It might be said, for example, that the UK and French armed forces have overall roughly the same levels capability. However, NATO's European allies collectively muster some credible firepower, although capability across countries is patchy.

Russian war-fighting capability has been much reduced by the Ukraine war, and it was estimated that could take it a decade to recover its former state of readiness. Whatever the outcome of the Ukraine war, in terms of territorial gain or loss for Ukraine, a NATO deprived of US political commitment, or even minus US membership, might muster enough military capability to offer a credible conventional military deterrent to Russia, provided more countries make the sort of increases in military expenditure being made by Finland, Germany, Poland and Sweden.

Conventional capability is not the whole of the story. There is also the question of the nuclear arsenals of NATO and Russia, in terms of tactical and strategic weapons.

Russian doctrine holds that low-yield tactical (or battlefield) nuclear weapons are “ a controllable part of a framework for achieving both battlefield results and war termination.’ President Putin recently pointed out that Russia had more nuclear warheads than NATO (including the USA), and described this as Russia’s competitive advantage”

The UK and France have strategic arsenals of submarine-launched nuclear missiles capable of deterring Russia from nuclear attacks on the UK and France. But nobody really believes that a tactical nuclear strike by Russia on, say, military bases or forces in the Baltic states or Poland, would attract nuclear strikes on Russian cities by the UK or France, whatever the legal pledges linking the parties. The UK has no tactical nuclear weapons at all. France has negligible capability for a graduated nuclear response, and anyway rejects the concept.   

Without the United States and unless there were increases in the nuclear weapons capabilities of France and the UK, Europe would have no response in kind to Russian use of tactical nuclear weapons. That would be quite an Achilles heel. Whether the US withdrew from NATO or not, a perception that America would not fight for Europe would shift the balance of power in favor of Russia

Whether a Trump Presidency went so far as withdrawing from NATO, or simply signaled a lack of commitment to fight for Europe, the result could be the same. In either event there could be a reduction in the 70,000 + US military personnel and their tactical nuclear weapons currently based in Europe. Disengagement would not happen overnight, and most bases, troops and equipment could actually stay in place, because the President might accept that they would be conveniently positioned for contingencies around the world. This could mean that US bases remained in place in countries such as Belgium, Germany, Italy, the Netherlands, Poland, Turkey and the UK.

A Trump Presidency would not necessarily hold all NATO allies in equal regard. The Kremlin might perceive that Washington would rush to the aid of some allies, but not others.

If the conduct of President Trump led the Russian leadership to believe that the United States would not automatically react to defend NATO allies against Russian attack, the balance of military power in Europe would shift in favor of Russia and against NATO's European allies, and some of those allies – such as the Baltic States  would feel at risk of Russian attack.

How would Europe respond?

President Macron – a champion of strategy autonomy would likely urge the EU to take on a larger defense role under French military leadership. The response of Member States is hard to predict, but EU funding could significantly increase the military capability of EU countries if it put modern weaponry in the hands of Member States most in need and least able to afford the outlay.

A European Defense Fund already exists designed to foster collaboration on developing capabilities and defense research, but its budget – €8 billion over 2021-2027 – is modest. By way of contrast, the United States has contributed  $ 47.7 billion worth of military aid to Ukraine since 2014. For a hypothetical “European Military Support Fund” to put, say, modern air-defense systems, ground to ground missile systems, and armored vehicles and tanks, in the hands of EU countries which needed them, would mean a multiannual plan and grants running into hundreds of billions of euros. This would in theory be achievable, if the political will be there, and the least painful way of achieving it might be common debt, loosely based on the model of the Covid Recovery Fund agreed in July 2020 – this involved €750 billion of common debt in 2020 values. Agreement on initiative this was hailed by then German Finance Minister Olaf Scholz as to “ Hamiltonian moment” meaning it was a step on the path to a United States of Europe. A European Military Support Fund could be a logical next step if the EU seriously wanted to achieve strategic autonomy from the US.

A greater difficulty would be securing unanimity. But this requirement could be side-stepped by using a procedure known as “enhanced cooperation” . This would allow EU Member States, minus detractors such as Hungary and Slovakia, to act in conjunction with the European Commission to finance a Military Support Fund through the issue of bonds.

A European Military Support Fund would not necessarily focus aid on the most needy Member States. It could reinforce the capability of those Member States with the best prospects of defending the territory of the EU from Russian aggression. It could – in theory – fund an increase in France's capability to deploy tactical nuclear weapons, and thereby provide a graduated response to Russian first use of tactical nuclear weapons against EU allies. France could offer to station tactical nuclear weapons in other EU Member States, just as Russia has stationed tactical nuclear weapons in Belarus. 

The EU as a whole would struggle to fill the security gap left by a wavering United States unless France extended its nuclear umbrella to cover the EU as a whole as well as its own territory. Yet this scenario seems unlikely.

The response of NATO

NATO and the EU have close links, including the fact that most NATO Members are also EU Member States. Whatever the reaction of the EU to de facto or de jure US withdrawal from the alliance, there would be a reaction on the part of Europe's NATO allies in their capacity as such. They would want to see the US return as soon as possible to its role as credible leader of the alliance and its security guarantor of last resort. They would be encouraged by some politicians in the United States – mainly but not solely Democrats – denouncing President Trump's disengagement from NATO and calling for a reversal of that policy.

Europe's NATO allies would likely reiterate their NATO commitments of mutual self-defense, and declare they would welcome the return of the US to its rightful place in the alliance at any time.

France and the UK, as Europe's major military powers, and nuclear armed powers at that, would likely assume some sort of substitute leadership role in NATO, but a consensus which included Europe's credible military powers would also be essential. Some at least of the allies already hosting US bases (Belgium, Germany, Italy, the Netherlands, Poland, Turkey and the UK) would be likely to continue to do so if that suited the plans of the US President, which it might well do. , for the reason mentioned above.

NATO without the de facto or de jure guarantee of US military support could hold together in the short to medium term, but its long term future would be problematic, because of Russia's overwhelming superiority in nuclear weapons.

The point has already been made that it is unlikely that France could or would extend the protection of its nuclear deterrent to the whole territory of the EU, and the same would be true as regards the territory of European NATO allies outside the EU (Albania, Iceland, Montenegro, North Macedonia and Norway). Nor would the UK extend the protection of its nuclear deterrent to the territory of its allies. The UK continues to maintain that its “minimum, credible, independent nuclear deterrent” is “declared to the defense of NATO,” and is essential to UK security and that of its NATO allies. But that does not mean and has never been understood to mean that the UK would launch a strategic nuclear strike on Russian cities in response to Russian use of nuclear weapons against a NATO ally.

What can be said is that Russia would likely exercise extreme caution in using nuclear weapons against any target in any European country close enough to the territory of France or the UK for targeting error or miscalculation to provoke a retaliatory attack by France and/or the UK , based on the belief in the latter countries that they were under nuclear attack from Russia. To that extent, the French and UK nuclear deterrents protect neighboring countries as well as themselves.


US withdrawal from NATO, or from an effective role in NATO, perhaps coupled with a Trump-brokered Ukraine “peace deal” letting Russia keep what it held, or a continuation of the war without US support for Ukraine, would be a victory for Putin and for his mission of reconstructing a version of the former Soviet Union. There would be some respite for NATO, as Russia rebuilt its armed forces and its depleted military stocks, but that respite could be short, as the Kremlin surveyed a weakened Europe, in which some voices would urge accommodation with Russia. 

Europe's NATO allies could muster and maintain credible conventional forces for collective defense against Russia if the political will be there. An enhanced defense role for the EU might provide a vehicle for some of the increased spending that would be needed on conventional forces, but the nuclear deterrents of France and the UK would not fully replace the nuclear umbrella of the United States.

That would make the European allies' best option a political campaign to bring the US back into NATO. But if that option failed, they would find themselves with a militarily dominant and assertive Russia to contend with. In the latter event, plans for Ukraine and Moldova and later Georgia, to join the EU would become problematic.

US withdrawal from NATO, in law or in fact, would create huge uncertainty, and could change the face of Europe. It is a sufficiently realistic possibility to justify planning at the highest level in NATO and the EU, although in ways that do not undermine confidence in US military leadership or forfeit the goodwill of a future Trump administration. Some of the most effective planning possible is already under way – increased military expenditure by at least some NATO allies, and investment in the sort of modern weaponry that has been used to such telling effect against Russian forces in Ukraine.


  1. Poland is building one of the West’s most muscle-bound militaries, on course to deploy more battle tanks than Britain, France, Germany and Italy combined. Poland is also a member of NATO and more than 10,000 American troops are stationed in Poland and 80% of military hardware heading for Ukraine passes through Polish transit points. Warsaw’s buildup is also a hedge against Trump return to the White House and that he will set NATO adrift.
  2. In Germany, Chancellor Olaf Scholz has committed the government to a long-term military expansion, at a cost of tens of billions of dollars annually throughout the 2030s.  If Donald Trump is elected, the Germans will see this as proof that they cannot rely on the USA for their defense, etc. Germany will push for a European army
  3. President Emmanuel Macron has embarked on France’s biggest military spending increase in a half-century, earmarking nearly $ 450 billion to boost outlays through the end of the decade by a third. His parallel effort to push Europe to take ownership of its security through better military and industrial coordination and less reliance on Washington’s weaponry and leadership


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