Republicans have a lot to say about the immorality of saddling the next generation with our national debt. But when it comes to leaving them a wrecked, depleted and rapidly warming planet, they are taking the exact opposite line. That’s especially odd when you consider how important that next generation is to the faltering GOP—and how broadly united those voters, known as Millennials, are in their concern over global warming and other energy and environmental issues. GOP leaders claim to be courting these young adults, but that apparently extends only to their use of Twitter and promises of a “hip-hop” party makeover...