Homicides are falling across the U.S. And that shift could impact the role crime — often a top voter concern — plays as an issue in November’s election. But it is a phenomenon for which experts don’t have a clear explanation. Some say homicide peaks come and go in cycles, some say policing improved after the COVID-19 pandemic, and some attribute it to the evolving national conversation about how to handle crime. A data analysis released last week shows that the number of homicides in cities like Boston, Philadelphia, Washington, D.C., and Chicago, are dropping. While many major cities, especially...