What would a second Trump presidency mean for UK-EU defence cooperation?


A Trump presidency would probably force the UK and EU to intensify their cooperation on security and defence. Fortunately, says Gesine Weber, this relationship was relatively less affected by Brexit. It would also push Europeans to have some difficult conversations about building on their own nuclear deterrent.



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The possible re-election of Donald Trump as US president is causing headaches for those working on European security – for good reason. The impact of another Trump presidency at this point could hardly be underestimated. Russia is waging war against Ukraine, and deterring Vladimir Putin is of the utmost importance for European security.

While US withdrawal from NATO, as Trump has threatened, would probably be a costly and a lengthy process, his election would prompt immediate uncertainty around US security guarantees for Europe. Europeans could no longer take it for granted that the US would defend them.

Because of structural problems that have existed for years — namely insufficient European defence budgets, a defence industry unfit to equip Europeans, and a lack of strategic preparation for the scenario of high-intensity war at the EU’s border — Europe is insufficiently prepared for a Trump presidency. Accordingly, reflections on “Trump-proofing” Europe mostly focus on the short-term need to continue supporting Ukraine and ensuring European defence. This includes ramping up production in the European defence industry, but also thinking about consultation mechanisms and scenario planning on what Europeans can, and cannot, achieve as security providers in their immediate neighbourhood.

Trump’s re-election would not only make it more urgent for Europeans to act on defence, but also directly affect the influence of individual European states in security and defence, and the role they will be expected to play. As one of Europe’s most capable players, the UK might have to step up to take the place of the US. A stronger role for the UK could also imply a window of opportunity for enhanced security and defence cooperation with the EU.

The potential for UK leadership

A Trump presidency would require all European states to step up — whether within NATO, the EU, in mini-lateral frameworks, and not least nationally. Alongside France, the UK is arguably the most capable European power in the field of security and defence, so decisions taken in London will naturally receive more attention from other Europeans. Indeed, the UK is well positioned to play more of a leadership role in Europe when it comes to security and defence. While London had already emphasised its willingness to be the “most capable ally in the Euro-Atlantic” in its Integrated Review in 2021, it confirmed that this was more than lip service with its swift and resolute action when Russia invaded Ukraine. In fact, the UK has played a “vanguard role” in supporting Ukraine, for instance through the early training of soldiers and the delivery of both heavy and highly technologically advanced weapons.

Furthermore, the UK has never actually cut defence ties with EU member states. The UK’s participation in the EU’s missions abroad naturally ended with Brexit, but defence cooperation in other formats continued: the UK has also heavily invested in closer ties in bilateral formats, such as bilateral ties or the Joint Expeditionary Force (JEF). In autumn 2022, the UK also joined the EU’s Military Mobility Project under the Permanent Structured Cooperation (PESCO), and NATO provides a central forum for exchanges on issues of European security. In fact, defence ties with Europeans were never affected as much by Brexit as other policy areas were, and operational cooperation and coordination on always continued on a practical level. In other words, the essential base for UK-EU defence cooperation never disappeared and remains an important starting point to build on in case of Trump’s re-election.

The impact of 2024’s elections

This base is a necessary but not a sufficient condition. A quantum leap to level up European defence will require political will on both sides of the Channel. The sequencing of elections in 2024 could encourage this political will: after the EU elections, a new EU Commission might take office just at the time when the UK has elected a new prime minister. After a (probable) Labour victory, one could expect London to seek stronger ties with Brussels.

While the composition of the next EU Commission and key portfolios is hard to predict, even a more conservative Commission is unlikely to turn away a UK which openly voices its willingness to cooperate in security and defence. The risk of US abandonment and a paralysed NATO puts both the UK and the EU at risk. Given these pressures, developing mechanisms for EU-UK cooperation (for example through plug-in options for the UK to the EU’s missions, or UK participation in the EU’s defence industrial base) would be in the interests of both Brussels and London. A “form follows function” approach seems reasonable for the first steps of defence cooperation: for the sake of efficiency and speed, the first steps could be achieved without a formal structure, but a formal security agreement would certainly be desirable in the medium and long term.

Time to talk nukes

The most pressing security challenge for the EU and UK, regardless of the US election result, is a joint approach to providing support for Ukraine and enhancing European capabilities. Yet a Trump presidency would also force Europeans to have a conservation that they have preferred to avoid over the past decades: the question of nuclear deterrence in Europe. It is almost impossible for Europeans to replace the US nuclear umbrella over Europe, given that US nuclear protection constitutes deterrence by denial — in other words, a nuclear attack on European NATO allies would entail disastrous retaliation, to the extent that such an attack would be extremely costly.

In contrast, the nuclear arsenals of the UK and France are much more limited, and constitute a model of deterrence by punishment, where a strike on Europe would lead to assaults on the attacker’s critical strategic targets. However, given the risk of abandonment by the US, Europeans would need to consider how they can strengthen nuclear deterrence in Europe themselves, for example through a structured nuclear dialogue. With France and the UK as nuclear powers and Germany involved in nuclear sharing with the US, a E3 proposal or initiative on the future of nuclear deterrence in Europe would be a good starting point.