If there is a “war on coal,” as Donald Trump and Sen. Mitch McConnell allege, it has been under way for a very long time. In Mr. McConnell’s home state of Kentucky, coal mine employment peaked at 75,633 in 1948. It fell by two-thirds to about 25,000 in the late 1960s, before doubling to more than 50,000 in the late 1970s. It has since fallen virtually without interruption and now stands at 6,465.

Much the same is true for West Virginia, the epicenter of Appalachian angst. The state’s coal industry employed close to 120,000...