The prospect of Donald Trump becoming US president again is causing great concern in the US and global climate scene. Unlike if Kamala Harris were to win the election, the consequences would likely be severe. At a time of escalating climate crisis and high geopolitical tensions, another US withdrawal from the international process would hit climate diplomacy hard. Although many observers are optimistic that the energy transition in the USA would continue under Trump, a Trump victory could jeopardize the future of the entire COP process internationally and pose major additional problems for COP29.