(CNN)The Rev. Martin Luther King Jr. liked to claim that the arc of the moral universe bends towards justice.
Over the long span of America’s often-racist history, you can make the case that King was right, but each lurch forward generates a reaction, transforming the arc into a sine curve.
Just as the end of slavery in the Southern states after the Civil War and Reconstruction produced the Jim Crow era, the election of the first black president has now produced the election of Donald Trump.
The United States has entered another backlash chapter, and we can probably expect more of them to occur over succeeding decades as we approach the demographic fault line where whites become a statistical minority in this country.