For two years American police departments have endured relentless attacks from the Obama administration, its media allies and the Black Lives Matter movement alleging that U.S. law enforcement is a racist, deadly threat to African-Americans. A handful of disturbing videos depicting police shootings helped galvanize widespread hostility to law-enforcement officers, and cops began backing away from the proactive policing that stops crime but has been repeatedly denounced as racial oppression.

The result, especially in the first...