Although China is also the world's largest exporter of CO2 (embedded in products and services), the US is still behind.
Current climate change really depends on cumulative historical CO2 emissions, where the US still leads.
Trump is most likely just trying to distract people from his Iran debacle, the cover-up of his involvement in the Epstein scandal, or whatever it is he's trying to do with the midterm elections. He's unlikely to follow through. It's better to wait and see what he actually does before taking any action.