The European Commission managed to dedicate 20 per cent of the 2014-2020 EU budget to climate mainstreaming despite the acute financial and economic crises. It then proposed a more ambitious 25 per cent target for the 2021-2027 EU budget, which was subsequently increased to 30 per cent in the negotiations with the European Parliament and Council. How did it manage to keep the EU's climate mainstreaming policy on track despite changing framework conditions including multiple crises? This article process-traces the European Commission's approach to increasing climate ambition in and despite turbulent times. It reveals that the Commission played a key role in maintaining the stringency of existing long-term goals through policy entrepreneurial leadership, mutual learning and relying on policy pathdependency from the 20 per cent mainstreaming target. This case has wider implications for theory highlighting the importance of policy entrepreneurs and learning in policy stabilization towards decarbonization.