Partisan shifts and external pressures: U.S. carbon governance under the EU’S CBAM

The European Union’s Carbon Border Adjustment Mechanism (CBAM) has introduced new external pressures that are reshaping U.S. carbon governance and further highlight persistent policy instability in climate governance for U.S. This article employs a panel multi-period difference-in-differences (DID) model and textual analysis as a complementary methodological framework to quantitatively and qualitatively evaluate the causal impact of CBAM on U.S. policy responses, especially before and after its introduction. This study defines the “post-CBAM period” as starting from the EU’s formal proposal of CBAM in December 2019, in order to analyze the corresponding adjustments in the U.S. policy agenda. The DID model uses state-level panel data (2016–2025) to isolate the causal effect of CBAM on climate policy enactment, while textual analysis of federal legislative documents identifies discursive adoption of EU regulatory terminology. Together, these methods provide robust empirical evidence that EU regulatory pressure has directly driven U.S. policy action. The findings reveal that U.S. carbon governance has exhibited a cyclical governance. Before the introduction of CBAM, federal carbon governance shifted from voluntary emissions reductions to stricter federal regulation and eventually moved towards weakening again. Following CBAM, the Biden administration promoted federal-level carbon reduction and subsidy-driven climate programmes, while the Trump administration tended to prioritise international bargaining and less stringent regulation of conventional energy in response to CBAM-related trade exposure. The study shows that federal policy will keep shifting with partisan change, while states and companies will gain importance in mitigation. This research underscores how external pressures shape domestic politics and offers recommendations for climate policymakers.