There’s nothing white supremacy can’t do. It is supposedly so pervasive and powerful that it can cause black men to sign up to serve as police officers in a majority-black city and beat up a black arrestee. It is to the contemporary left what capital was to Marx, sex was to Freud and gravity was to Newton. It is the “King Charles head” of American public life — a matter of obsession that comes up in debates and contexts where it has no possible relevance. A CNN opinion piece by former Obama official Van Jones was headlined “The police who...