The defining photograph of the attempted insurrection on Jan. 6 was that of a man strolling through the broken halls of our national Capitol, amid the smashed windows and assorted rubble of the failed coup, proudly brandishing a Confederate flag on his shoulder and hoping to overturn an election decided largely by Black voters. It’s an image that tells the story not only of Jan. 6 or of the Trump presidency, but also of all the steps that led to that moment — the whole history of hate in America captured in one frame. This deadly connection between white supremacy...