Republicans and Trump are a red herring. The Paris Accord simply sets a goal. It does not tell how how to get there or commit resources to achieving that goal. Actually keeping climate warming to 2C is going to cost tens of trillions of dollars: https://www.technologyreview.com/s/527196/how-much-will-it-c.... No Democrat in the foreseeable future would have made that investment either. Participating in the Paris treaty is simply an empty feel good gesture.