Several politicians have vaunted a muscular but myopic plan for dealing with the fentanyl crisis: to eliminate sources of the drug near the U.S.-Mexico border through the use of military force. The fentanyl crisis is being portrayed as an international conflict, not a failure of domestic policy, but a problem entirely caused by the evil members of Mexican cartels who, it is being claimed, deserve to die, along with, apparently, anyone who happens to be at their side. But even assuming, against an abundance of evidence from history, that the deployment of military force would have any effect...