Last Wednesday, over the course of three and a half hours of arguments, the conservative and liberal justices on the U.S. Supreme Court jousted over whether to overrule a 40-year-old case called Chevron v. National Resources Defense Council. The Chevron case is famous among lawyers—it’s among the most cited cases of all time—because it established the principle that the courts should defer to federal agencies when they interpret the law in the course of carrying out their duties. That may not sound like a big deal, but it is. Chevron shields the executive branch from overly intrusive court review, giving it the flexibility to do its work. But the case is under threat. Conservative justices on the Supreme Court want to dismantle Chevron, believing that deference is improper because courts—not federal agencies—ought to say what the law is. They may have the votes to scrap the case outright; if not, they will almost certainly narrow its scope. Ben Johnson: The little known rule change that made the Supreme Court so powerful Naturally, much of the …