Rev. Al Sharpton called for national policing legislation akin to the Civil Rights Act this morning at the kickoff his National Action Network’s annual convention, just after the arrest of a white South Carolina police officer for murder in the shooting of an unarmed black man. “There must be national policy and national law on policing,” Mr. Sharpton said. “We can’t go from state to state, we’ve got to have national law to protect people against these continued questions.” Mr. Sharpton’s comments, coming on the heels of multiple instances of police killings of unarmed men of color around the country,...