The G.O.P. should take the wise counsel of Andy Karsner, who was George W. Bush’s assistant energy secretary and one of his climate negotiators, and use the Paris deal to build a bridge back to constructive engagement on the subject. The G.O.P. can plausibly argue, said Karsner, that it was Bush who, in 2007, created the “major economies” strategy to address climate change through precisely the kind of market-enabled, voluntary national targets adopted in Paris