Despite Kamala Harris’ recent anointment as the new Democrat presidential candidate following Biden’s withdrawal therefrom, Trump’s reelection remains nevertheless a credible prospect. As such, a once-unwavering Euro-Atlantic relationship is still in peril. Though Europe managed to weather an already-difficult first Trump presidency, a second is all but certain to hit harder. A turbulent European political landscape and two far-reaching wars have already set the scene for whoever is inaugurated into the White House come January. Add to it a questionable American backing for Ukraine, a doubtful US adherence to NATO’s mutual defence clause, and a punitive US trade policy on a European economy dependent on exports to North America, and Europe will additionally face its ‘biggest test in transatlantic relations in postwar history’, were Trump to be reinstated.

With Biden still in office, both Washington and Brussels are gearing up for this prospect. Yet, little of Trump-proofing the Euro-Atlantic partnership can prepare the EU for what may soon be an existential risk to its unity. Were American leadership to wither, EU leaders will be forced to face dire dilemmas regarding the future of an ever more isolated and internally-fragmented bloc.

NATO and Defense

The 75th anniversary of the longest-standing military alliance in history may have very well been a time for homage were it not overshadowed by US internal politics. As NATO heads-of-state gathered in Washington in July formally to commemorate the milestone, the prospect of Trump leading the organisation’s backbone loomed ‘over every conversation’ at the summit, as said by an Eastern European diplomat.

Asked by the Washington Post if Trump was a recurring topic of conversation behind-the-scenes among European leaders, Norwegian Prime Minister Jonas Gahr Støre replied ‘you will not believe me if I said no’.

Long-term pledges seeking to safeguard — or rather ‘Trump-proof’ — the alliance’s commitment towards Ukraine’s defence have hence taken precedence. NATO leaders have agreed to shift responsibility for coordinating Ukrainian military support from the United States’ Pentagon to Germany’s southern city of Wiesbaden — unofficially seen as an attempt to strip leverage from a future Trump presidency. Ukraine was declared on an ‘irreversible path’ towards NATO membership. The US announced the deployment of longer-range missiles in Germany in 2026 to bolster Russian deterrence — a formerly-banned move under the 1987 Intermediate-Range Nuclear Forces Treaty which ended in 2019. A commitment of €40 billion in donations to Ukraine during 2025 was issued. And though in practice non-binding, the US has also signed a 10-year bilateral security agreement with Ukraine, outlining a decade-long framework for military assistance and cooperation. Add to this a series of short-term pledges such as the Dutch-Danish transfer of F-16 fighter jets and the US consignment of new air defence systems to Ukraine, and Kyiv received most of what it was asking for in July.

Moreover, with Jens Stoltenberg’s term as Secretary-General coming to an end, NATO allies officially decided to — prior to the summit — entrust the alliance’s helm to Netherlands’ Mark Rutte starting October, a veteran Dutch Prime Minister who’s reputation has proven him effective in managing repeated tense interactions with Trump.

The US has also taken independent steps to Trump-proof the country’s NATO membership. In December 2023, the US Congress approved legislation that would bar any future president from unilaterally withdrawing from the alliance. That said, it would not require US withdrawal for NATO’s mutual defence provisions to become, practically-speaking, trivial. A Trump presidency, accompanied by a far less-establishment and more ‘Trumpian’ cabinet than last term — as suggested by Trump’s vice-presidential pick JD Vance —, will likely have enough of an executive power over US foreign policy for day-to-day European security assurance to be even more unpredictable — especially regarding Ukraine.

Of course, there are also those who argue a second Trump term shouldn’t be seen as extraordinarily nerve-racking. ‘Stop freaking out about Trump. You’ve done this before… and guess what? It actually wasn’t that bad for Europe,’ said Rachel Rizzo, a nonresident senior fellow at the Atlantic Council’s Europe Center. Additionally, not all NATO leaders express equal anxiety over Trump, particularly right-wing European heads-of-state such as Italian Prime Minister Giorgia Meloni and Polish President Andrzej Duda. The Italian ambassador to the US encouraged calm by stating that NATO’s core principles can withstand election cycles. And as said by Jacek Siewiera, the head of Duda’s National Security Bureau, Trump and Duda ‘are friends… they understand their values’.

Stoltenberg also offered reassurance to the Trump worry, saying in a press conference that ‘the main criticism from former president Trump… has not primarily been against NATO, it has been against NATO allies not investing enough in NATO, and that has changed’. That is true, and Trump himself told Fox News Radio ‘I just want them to pay their bills. We’re protecting Europe. They take advantage of us very badly’.

Still, efforts to portray strong unity within NATO have increasingly been met with political splinters in parts of the alliance other than from the US. Indeed, Hungarian Prime Minister Viktor Orban and Slovakian Prime Minister Robert Fico continue to express soft views towards Moscow — a divergence equally felt within the EU. The question remains as to the extent of their (re)emboldening if Trump were to be reinstated.

Energy, Trade, and Digital Security

Anxiety is likewise brewing over the future of US-EU trade — a concern fueled by the effects of Trump’s ‘America first’ agenda during his first term. This time around, however, the European Commission is determined not to get caught off guard, not least because the stakes have just gotten far higher.

As said by one official of the institution, ‘the Commission is setting up a structured internal process to prepare for all possible outcomes from the U.S. presidential election’. Still, only time will tell whether Europe can truly muster a comprehensive framework effective at averting the worst effects of a second Trump trade policy destined to threaten various susceptible EU sectors, from energy to digital security.

With the US having partly replaced Russia’s former role as European energy supplier following the war in Ukraine, the EU has nearly doubled its dependence on US gas, now accounting for 50 percent of its LNG imports. The extent to which Europe can bypass an energy-hostile United States by speeding up a green energy transition already in full-throttle is up for debate, but is worth looking into, as suggested by various think tanks.

As for digital security, the EU is likewise particularly exposed as it manufactures little of its cloud-computing systems and telecommunications infrastructure, sectors highly dependent on American and Chinese products. Such services are vital as they support virtually every part of internet use, from data storage to networking. In light of their security importance and Europe’s foreign dependency for them, some European states such as France, Italy, and Spain are now implementing policies which would require firms providing said services to store European data on EU soil and to host their headquarters within the EU — and it may be wise for the EU at large to follow suit.

More generally, Trump’s former ‘trade war’ is likely to reignite if he is reelected starting with a universal 10 percent import tariff on all EU goods entering the US, as already suggested by the former president in an interview with Fox Business.

The EU-US Trade and Technology Council (TTC), a forum established in 2021 by the Biden and von der Leyen administrations to heal a scathed trade relationship between both countries following Trump’s presidency, will hence likely falter under a second Trump administration despite attempts to prove otherwise.

In an interview with CNN, president of the European Central Bank, Christine Lagarde, suggested that the best way to protect a vulnerable Europe from a second Trump term would be to bolster its single market. This would theoretically include, for instance, greater integration of financial markets for facilitated investment into small businesses in order to incentivise greater innovation. ‘The benefit of being more [of] and really a single market is tremendous and I think we have to just move in that direction. That’s how Europe moves, by the way, when it is under threat,’ she added.

Conclusion

Trump’s increasingly likely reelection has indisputably stirred up oversee anxiety, not least from an exposed Europe. With an EU-friendly administration still in the White House, efforts to future-proof the transatlantic partnership are running on overdrive, taking advantage of an ever shortening time budget. Still, these efforts have largely centred on security and military cooperation, most likely because of the more war-prone global context. However, some rather concerning military-related prospects are arguably not receiving the attention they warrant, particularly the possibility of a weakened American nuclear umbrella over Europe under Trump. Will the UK and France have to take greater responsibility to maintain a credible Russian nuclear deterrence over Europe, and will reluctant states, such as Germany, get on board with said countries doing so? Time will tell.

Worries over the economic effects of a new ‘America first’ agenda affecting Europe are likewise not to be dismissed. The EU has much to lose from a trade-hostile US, especially in areas such as energy and digital security — areas which are harder to ‘Trump-proof’, unlike NATO. Weathering a second Trump term will thus depend on the willingness of Member States to unify on common EU trade and foreign policies requiring hard decisions. Though it seems like a futile endeavour under the current politically fragmented European context, a Trump reelection just may be the much awaited wake-up call desperately needed for the Union.