THE UNITED STATES prides itself on being a society ruled by law. The country is governed by a constitution, not by a king or by military might, and all citizens are expected to obey its laws, which are made by the people's elected representatives. No one, neither the president nor anyone else, is above the law. Moreover, a government based on the rule of law does not subject its citizens to the uncontrolled use of force.

Americans give their police the right to use physical force to protect the people who live by the laws that apply to all citizens. The police do not have an unlimited right to use unlimited force, however. Officers must follow laws and stick to policies that state how much force can be used in various situations. When police use unnecessary force, they may be...