A number of historians and political analysts have come forward to point out that the USA is falling into an old political trap: divide and conquer. We are an increasingly polarized nation, treating each other as if we're fans of opposing sports teams rather than a whole society looking to its best interests. As the left and right move apart, they leave a gap in which a demagogue fits perfectly.

Human nature lends itself to tribalism, but a nation needs to see itself as a tribe or it will fall...