Could Trump really take the US out of NATO?

Analysis: Whether a US president could unilaterally terminate or withdraw the US from a treaty remains a matter of constitutional debate

Speaking to a joint session of the US Congress last week, Britain’s King Charles made pointed references to the importance of the North Atlantic Treaty (NATO) as the alliance grapples with repeated threats from its most powerful member to simply walk away. But could Donald Trump take the US out of NATO? And, considering multiple recent climbdowns, will he? Or is this all part of his negotiation strategy?

The US president has taken a markedly transactional view of the alliance, which he had threatened to abandon already during his first term. In 2016, while still a presidential candidate, Trump stated that the US would only intervene to defend those allies who had met the 2% defence investment pledge agreed at the 2014 Wales Summit. At his first NATO Summit as president in 2018, he threatened to abandon NATO unless allies met the defence spending target by 2024. Trump has also repeatedly questioned the benefits of NATO membership for the US.

Since moving back into the Oval office, he has pushed allies to agree at the 2025 Hague Summit to raise defence spending to 5% by 2035. At the same time, he also considered relinquishing the position of Supreme Allied Commander Europe (SACEUR), a postion which has been held by an American senior military officer ever since its establishment in 1950, to Europeans. Trump has also considerably shaken trust in the alliance by insisting on the need for the US to annex Greenland, citing national security concerns and Denmark’s alleged inability to stop Russia and China in the region. He also threatened to impose further 25% tariffs on any European allies who opposed him.

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From RTÉ Radio 1’s Morning Ireland, King Charles makes case for stronger ties between Britain and US

Trump’s actions and rhetoric are already significantly damaging the credibility of Article 5, on which the alliance’s deterrence posture is largely based. However, a sudden and swift US withdrawal from NATO could have disastrous consequences.

While NATO provides neither a suspension clause nor infringement procedures that the US could use against other members – as Trump has threatened to do in relation to Spain – it does allow for withdrawal under Article 13. This provision, although never triggered, allows any party to leave the alliance one year after giving notice. Unlike Article 11, which explicitly requires that ratification be carried out in accordance with each member’s constitutional processes, Article 13 makes no reference to internal constitutional procedures.

The problem is that the constitutional process for treaty withdrawal in the US is not as straightforward as that for ratification. Article 2 § 2, cl. 2. of the US constitution expressly requires a two-thirds majority in the US Senate for the president “to make Treaties”. However, it is silent on whether the Senate has any formal role when it comes to unmaking treaties. Whether a US president could unilaterally terminate or withdraw the US from a treaty remains a matter of constitutional debate. To complicate matters further in the case of NATO, the US president is also the commander-in-chief of the armed forces, which gives the executive branch significant control over military commitments in practice.

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Congress has adopted important legislative steps since Trump’s first presidential election victory to restrain the president from abandoning NATO. Following Trump’s threat to leave at the 2018 Brussels Summit, the 2019 NATO Support Act was introduced and passed in the US House of Representatives in January 2019 by a vote of 357 to 22. The bill sought to prohibit the use or appropriation of funds for the purpose of withdrawing from NATO. The bill also stated that Congress did not consider Goldwater v. Carter to be controlling legal precedent with regards to US withdrawal from treaties.

In 1979, then-president Jimmy Carter had moved to terminate the 1954 mutual defence treaty with Taiwan without seeking congressional approval, following the shift to the “one China” policy and efforts to normalise relations with Beijing. Senator Barry Goldwater and others challenged the decision, but the US Supreme Court eventually dismissed the case, with a plurality of justices expressing the opinion that it raised a political question or was not ripe for judicial review. The ruling left unresolved the question of whether a US President may unilaterally terminate treaties, effectively leaving the issue to the political branches to sort out.

The 2019 bill also mentioned that it was the policy of the United States to oppose any efforts to withdraw from NATO, whether directly or indirectly, including by reducing contributions to NATO structures, activities or operations in a manner amounting to a de facto withdrawal. Although the bill did not advance within the Senate, it was reintroduced in 2023 and later incorporated as an amendment in the National Defence Authorisation Act (NDAA) for the Fiscal Year 2024.

From RTÉ Radio 1’s Morning Ireland, will the US leave NATO?

The 2024 NDAA provides in Section 1250A that “the President shall not suspend, terminate, denounce, or withdraw the United States from the North Atlantic Treaty”, nor use funds for that purpose without the advice and consent of two-thirds of the Senate or an act of Congress. On this basis, if Trump decided to withdraw the US from NATO, Congress could challenge the decision claiming a violation of Section 1250A of the NDAA.

But in 2020, when Trump withdrew from the Open Skies Treaty, the US Department of Justice’s Office of Legal Counsel published an opinion concluding that requiring notification 120 days in advance unconstitutionally restricted the president’s authority to execute the rights of the United States under treaties and to conduct diplomacy.

It is unclear how the US Supreme Court would rule – would it side with the executive or with the legislative branch – if it were asked to decide on the merits of a case concerning a president’s decision to unilaterally withdraw from NATO. In reality, the court is far more likely to avoid the issue altogether, as it has done before in cases like Goldwater v. Carter.

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This reluctance may be reinforced by the increasingly politicised nature of judicial appointments, which risks undermining the Court’s perceived independence and its willingness to act as a robust check on the political branches. It is not even clear whether Congress would bring a lawsuit over such a decision, reflecting broader uncertainty about how far the legislative branch is willing or able to escalate inter-institutional conflicts in a highly polarised environment.

But what is certain is that a decision to leave NATO, whether later challenged or not, would immediately be read in Moscow and European capitals as a decisive break with long-standing US commitments to European security. The strategic signal would land first, with any court rulings coming later, if at all.

Of course, Congressional oversight can play a role in constraining presidential action. Testimony like that of former SACEUR General Christopher Cavoli to the Senate Armed Services Committee last year, warning of the consequences of relinquishing the position of SACEUR, shows that senior military officers can still shape the debate in Washington.

Bipartisan Congressional support for NATO, coupled with strong pushback from military and intelligence circles, can materially raise the political cost of withdrawing from the world’s most powerful Alliance, even if it cannot eliminate the existing constitutional uncertainty. The real question is not whether Trump can leave NATO, but whether we are ready to find out.

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The views expressed here are those of the author and do not represent or reflect the views of RTÉ

Could Trump really take the US out of NATO?

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