The US is the largest developed economy and has some of the high per person emissions in the world. It’s hardly going to be possible for another country to have a larger fall if it’s five times smaller with half the per person emissions.

The other point is this relies on fracking, and the carbon intensity of fracking depends on the level of escaped Methane. It can actually be worse than coal. And Trump has just reversed a lot of the regulation which prevented venting of Methane from fracking sites.