Of course, the Trump administration is not just tearing up car efficiency standards but an entire suite of global-warming rules that President Barack Obama approved, including on power plants, oil and gas production, and other industrial activities. Taken together, the impact of these policies on the planet’s future would have been significant. True, it would not have been nearly enough without commensurate effort on the part of other countries. But U.S. participation in the Paris global-warming agreement, the world’s best chance to get all major polluters moving together to cut emissions, would have helped bring other countries along. And President Trump pulled the United States out of it, too. Once the exit is official, the United States will be the only country in the world not party to the pact. If catastrophic warming materializes, it will be in part because of the ruinous choices the Trump administration has made over the past two years.