Trump and NATO 2026: What US Foreign Policy Means for European Security

Last updated: June 2026  ·  9 min read

The relationship between the United States and NATO has been a defining feature of the post-World War II international order. Under the second Trump administration, that relationship is being stress-tested in ways that are reshaping European security assumptions, defence spending trajectories, and the strategic calculus of every NATO member.

This article examines what has actually changed in the US-NATO relationship since 2025, the three scenarios analysts are tracking for 2026 and beyond, and how forecasters and prediction markets are pricing the risk to European security.

What Has Actually Changed Since 2025

Trump’s second term has produced a more systematic challenge to NATO’s foundational assumption than his first. In 2017–2021, the complaints about burden-sharing were loud but the institutional machinery of the alliance largely absorbed them. In 2025–2026, the approach has been different in three key ways.

First, the administration has explicitly questioned Article 5 — the collective defence clause — by suggesting that it is conditional on members meeting their spending commitments. This is a departure from previous US administrations, all of which treated Article 5 as an unconditional commitment regardless of burden-sharing disputes.

Second, the administration has negotiated separately with Russia on Ukraine and European security without treating NATO as the primary framework. This has created anxiety in Eastern European members who see bilateral US-Russia dealmaking as potentially trading their security interests for other priorities.

Third, the domestic political coalition supporting the Trump administration is more sceptical of foreign commitments than previous Republican coalitions. The institutional pressure that moderated Trump’s NATO approach in his first term — from within the Pentagon and State Department — has been reduced as those institutions have been reshaped.

Europe’s Response: Accelerated Autonomy

European NATO members have responded with the fastest increase in defence spending in decades. By mid-2026, a majority of European NATO members are at or above the 2% GDP target — a significant shift from the situation in 2024 when only a minority met the threshold. Germany, traditionally resistant to large defence budgets for historical reasons, has passed a major constitutional reform enabling sustained military spending above the debt brake constraint.

The European Union has also moved toward a more unified defence posture, with new procurement frameworks, joint capability development programmes, and the beginnings of a European strategic autonomy doctrine that is explicitly designed for a world where US commitment is less automatic.

The irony is that Trump’s pressure has achieved what decades of US diplomatic effort could not: a genuine increase in European defence investment. The question is whether this represents a healthy rebalancing of the alliance or the beginning of a decoupling.

Three Scenarios for US-NATO Relations in 2026

Scenario 1: Managed Conditional Alliance (Most Likely)

The US remains inside NATO but the alliance operates on an explicitly transactional basis. Members that meet spending targets receive strong signals of US commitment; those that don’t face uncertainty. European states continue accelerating defence spending and developing autonomous capabilities. The alliance formally holds but its character has changed fundamentally — from a values-based collective security arrangement to a transactional defence partnership. This is the scenario most forecasters currently consider most likely, and is arguably already underway.

Scenario 2: Partial US Withdrawal or Reduced Forward Presence

The administration reduces US troop presence in Europe — particularly in Germany and Poland — as a cost-cutting measure or as leverage in NATO burden-sharing disputes. This falls short of formal withdrawal from the alliance but materially changes the US military footprint. European states respond with urgency but the capability gap created cannot be filled in the short term. This scenario is considered plausible (15–25% probability) and would significantly change the security calculus in Eastern Europe.

Scenario 3: US Exit from or Effective Departure from NATO

A formal US withdrawal from NATO, or a withdrawal in all but name through non-participation in collective defence planning. Most analysts consider this unlikely in 2026 — the institutional and legal barriers are significant, Congress has passed legislation making unilateral withdrawal harder, and even within the Trump administration there is institutional resistance. But it cannot be excluded as a tail risk scenario, particularly if a major crisis tests the alliance’s cohesion and the US response is seen as inadequate.

The Ukraine Connection

The US-NATO relationship cannot be understood in 2026 without the Ukraine dimension. The Trump administration’s approach to the Russia-Ukraine conflict has prioritised a negotiated settlement over continued military support. US weapons deliveries to Ukraine have become more conditional, tied to progress in peace negotiations rather than the unconditional support framework of the Biden administration.

For European NATO members, this creates a dilemma. They have continued and in some cases increased their own support for Ukraine, but the reduction in US support has changed the military calculus on the battlefield. European states that had been relying on a joint Western approach are now managing an increasingly independent European position — a role they were not fully prepared for structurally or politically.

The broader implication is that any Ukraine settlement negotiated by the Trump administration will be evaluated in Europe for what it signals about US willingness to trade European security interests for other priorities. A settlement that leaves Russia with significant territorial gains and without accountability would be interpreted by Eastern European NATO members as a dangerous precedent.

What Prediction Markets Are Pricing

Conclusion: A Changed Alliance, Not a Broken One — Yet

NATO in 2026 is a different institution from NATO in 2024. The unconditional US commitment that underpinned European security planning for 75 years has been replaced by something more contingent, more transactional, and more uncertain. This is not a collapse of the alliance — but it is a structural change that European security architectures will need to adapt to.

The silver lining — if there is one — is that the pressure has accelerated European defence investment that was genuinely overdue. The question is whether Europe can build the capabilities it needs before the next major crisis tests whether the alliance still means what it once meant.