This month, more Mine-Resistant Ambush-Protected vehicles (MRAPs) have found their way from the wars in Afghanistan and Iraq to the Main Streets of America. These are just the latest acquisitions in a growing practice by Pentagon that's militarizing America's municipal police forces. Police departments in Boise and Nampa, Idaho, each acquired an MRAP, as did the force in High Springs, Florida. The offer of war-ready machinery, at practically no cost, has proven hard to resist for local police departments. Increasingly, they are looking like soldiers equipped for battle. The growing similarity between our domestic police forces and the U.S. military...