Managing the Transatlantic Relationship in the Absence of US Leadership: Understanding the Trump Administration’s National Security Strategy

The Trump administration’s December 2025 National Security Strategy (NSS) represents a radical shift in US foreign policy, involving a move from global leadership of a rules-based international order to unabashed nationalism and regional hegemony. The new strategy no longer views the country’s sprawling network of alliances and partnerships and its ability to attract and integrate high-level talent from around the world as unique strengths, but rather as vulnerabilities to be mitigated. 

However, as jarring as these substantive changes are, the document’s structural changes and the irregular process that produced it may prove more significant in demonstrating just how sharply Washington is turning away from 80 years of bipartisan foreign policy consensus. The change is evident not just in the Trump administration’s policies, but – crucially – in the decision-making process that produces them. The new NSS is best understood as the formalisation of the administration’s abandonment of traditional policy coordination and strategic planning itself, an effort that has included the removal of senior career diplomats, military commanders, and intelligence officers; the systematic dismissal of senior judge advocates general and inspectors general; and the firing of many National Security Council (NSC) staff. The collective result of these steps, which find their natural culmination in the NSS and the National Defense Strategy (NDS) that followed in January 2026, is a policymaking process that is less informed by objective intelligence and analysis, less constrained by legal and policy advice or alliance consultation, and thus more subject to impulsiveness and ideological influence. Both of these developments – a new “America First” nationalism that eschews multilateral constraints and an erratic decision-making process that produces unpredictable and often impracticable outcomes – require a fundamental assessment by the country’s partners of their approach to the United States, both bilaterally and within established multilateral frameworks.

This Policy Brief examines the practical implications of the 2025 NSS and the dramatically changed decision-making process it represents. For transatlantic allies and other middle powers, the central question is no longer whether US strategy has changed, but how to operate effectively in an environment of reduced predictability and diminished US strategic anchoring.