This article undertakes a comparative analysis of European Union security and external economic policies to explore the different trajectories of strategic autonomy (SA) in these two domains. In so doing, it contributes to a better understanding of endogenous drivers of policy change in response to geopoliticising pressures. Drawing on discursive institutionalism, it analyses three dimensions of ideational power: power in, power through and power over. The evidence, based on documentary analysis and interviews, demonstrates that though SA presented a more significant challenge to pre‐established paradigms in external economic relations, the role of the Commission as an ideational entrepreneur, supported by its coercive power, facilitated the adoption of the idea of (open) SA. Conversely, French President Emmanuel Macron was unable to persuade others of the adoption of a sovereigntist conception of SA in security, with the exception of defence industrial policy, where the Commission enjoys budgetary power and competences.