The contest for the Democratic nomination is being largely portrayed as an historic confrontation between the first ever electorally-credible African American and the first ever electorally-credible woman running for president of the US. That in itself is sufficient to warrant blanket coverage, consuming interest and at times hysterical commentary on what is without question an unprecedented contest.

However, all of the coverage is missing what is most fascinating about this race. It is not the biographies of the two remaining Democratic candidates, or the number of voters who have been energised by the primary process, but the way in which the rivals are erasing and redrawing the lines of demarcation that exist within the Democratic party.