FBI Director James Comey has again defied the official White House line on policing and the Black Lives Matter movement. The “narrative that policing is biased and violent and unfair” is resulting in “more dead young black men,” Mr. Comey warned in an Oct. 16 address to the International Association of Chiefs of Police in San Diego. That narrative, he added, also “threatens the future of policing.”

Mr. Comey has spoken out before. In October 2015, after he observed that rising violent crime was likely the result of officers...