Climate change is a global challenge requiring ambitious action by all the world's countries. The Paris Agreement is meant to bind together international efforts to reduce temperature increase to well-below 2°C in comparison to pre-industrial levels and pursue efforts to limit temperature increase to 1.5°C. Insufficient ambition to achieve this goal is however pervasive across the signatories of the Paris Agreement-the Nationally Determined Contributions (NDCs), put forward in 2015, set the

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... d on a path that is, unlikely to limit global temperature increase to well-below 2°C (Climate Action Tracker, 2020; Fawcett et al., 2015; Rogelj et al., 2016) , let alone 1.5°C. New NDCs will be put forward soon, presenting an opportunity to ratchet ambition and actions upwards. In the second half of 2020, several major emitters set the tone with enhanced mitigation targets: the E.U. stated that it will reduce greenhouse gas (GHG) emissions in 2030 by 55% compared to 1990 instead of its initial reduction target of 40%; China pledged to become carbon-neutral before 2060, a timing that could be compatible with 1.5°C consistent global emission pathways (Robiou du Pont et al., 2016) . Japan, South-Korea, the United Kingdom, and Canada also put forward net-zero goals for 2050 (Climate Action Tracker, 2020). During the Trump Administration, the U.S. remained on the sidelines as other countries took leadership. More broadly, the stance of the U.S. federal government on climate change has been inconsistent over the last three decades and characterized by partisan polarization on environmental policy (Dunlap et al., 2016 ). Yet the U.S. plays a critical role in international climate ambition. The U.S. is the world's largest economy and second-largest GHG emitter, accounting for 12% of global GHG emissions in 2017 (Climate Action Tracker, 2020). Equally importantly, U.S. leadership has had an important influence on climate negotiations