Bigfoot. The Loch Ness Monster. Batboy. Throughout time there have always been those who insist they have seen mythical creatures, people who swear to the existence of phenomenon for which scientists say there is no tangible evidence, only hearsay, fable, legend.

But unlike the Abominable Snowman, scientists say the Spine of the Democratic Party is more than a myth. Incredible as it seems today, the legend of Democratic Backbone is based on historical fact, says Prof. Wendy Heep,...