In February of 2003, then-aspiring Democratic presidential candidate Howard Dean got applause at a Democratic National Committee meeting when he argued that “white folks in the South who drive pickup trucks with Confederate flag decals on the back ought to be voting with us.” More than a decade later, in the wake of the violent white supremacist rally surrounding a statue of Robert E. Lee in Charlottesville, Virginia, last wekend and President Trump’s full-throated defense of Confederate monuments, the politics have changed. What used to be a series of low-key, local fights has turned into a party-defining wedge issue with...