President Obama on Thursday signed an executive order officially creating a “Task Force on 21st Century Policing,” a high-level group that will report directly to the president with recommendations on how to strengthen ties between law enforcement and the communities they serve. Mr. Obama first announced the task earlier this month on the heels of unrest in Ferguson, Missouri, and New York City, where the deaths of black men at the hands of police officers further fractured ties between police departments and citizens. The task force will be chaired by Philadelphia Police Commissioner Charles Ramsey and Laurie Robinson, a professor...