This paper investigates whether left-leaning politicians are more effective than their right-leaning counterparts in reducing deforestation in the Legal Amazon in Brazil. Using data from 760 Amazon municipalities and a regression discontinuity approach based on close elections, it finds that leftist mayors tend to increase environmental spending always and may reduce deforestation, though the latter effect are uneven and do not extend to reforestation outcomes. Their impact is stronger in contexts with fewer coalition constraints, greater fiscal autonomy, and certain geographic or political conditions. While electoral dynamics often bring environmentally focused candidates to power in high-risk areas, structural and economic pressures limit mayoral ability to achieve sustained reductions in forest loss. Overall, the findings highlight both the potential and the constraints of decentralised governance in advancing environmental protection and carry implications for subnational environmental policy not only in Brazil, but also beyond its border.