The lawyers who designed the Paris Agreement (many of them American) were highly aware of US electoral schedules. That’s why they made the process for exiting the Agreement take four years. Trump may have announced the US’s intention to leave yesterday, but it won’t take effect until 4 November, 2020. And he is up for election on 3 November, 2020. In other words, the decision to leave Paris doesn’t belong to Donald Trump. It belongs to every American who votes in 2020.