Why is Middle America killing itself? The fact itself is probably the most important social science finding in years. It is already reshaping American politics. The Post's Jeff Guo notes that the people who make up this cohort are "largely responsible for Donald Trump's lead in the race for the Republican nomination for president." The key question is why, and exploring it provides answers that suggest that the rage dominating U.S. politics will only get worse. For decades, people in rich countries have lived longer. But in a well-known paper, economists Angus Deaton and Anne Case found that over the...