Mammoth litigation over a pillar of the Obama administration’s climate-change policy goes before the full U.S. Court of Appeals for the D.C. Circuit today. And depending on your point of view, the so-called Clean Power Plan is either a “blunderbuss” and “power grab,” or a classic “exercise in cooperative federalism.”

The Clean Power Plan imposes the first national limits on carbon pollution from power plants—the largest source of those emissions in the country. The U.S. Environmental Protection Agency on Aug. 3, 2015, finalized the Clean Power Plan rule and published emission guidelines for states to follow in developing plans limiting carbon emissions from existing plants.