President Trump had a profound, largely adverse impact on environmental and climate policy, both domestically and internationally. In addition to rolling back environmental regulations and related policies, Trump sought to undermine the institutions and core values undergirding environmental and climate protection. This article analyses Trump’s environmental tenure and legacy, examining key policies and regulations, but also norms, values and discourse. Drawing on insights from new institutionalism, the article explores three different dimensions of Trump’s potential environmental legacy – organisational, policy and ideational. For each it identifies the institutional and discursive factors shaping Trump’s impact, its “stickiness” and durability. It then analyses attempts by the Biden Administration and others to counter, reshape or chip away at that potential legacy. Re-visiting and adapting core institutionalist assumptions, the analysis suggests a decisive factor determining Trump’s legacy is not his own actions and narrative but rather how – and how successfully – other institutional actors support, spread or counter them. The article finds that while Trump’s impact on organisations, regulations and even policies can be diluted (and his legacy diminished), Trump’s attack on the norms and trust underpinning environmental action may be more long lasting.