Suppose, for a moment, that Trump gets what he wants: the USA leaves the World Trade Organization and NATO. What would be the effect on the US domestic economy? What seems likely to me is that living in that America would become very much like living in the old Soviet Union; we will work very hard for poor wages and be asked to patriotically bless the most awful products of American industry, while the rest of the world forges ahead.
Meantime, environmental degradation will continue. The seas will continue to rise.