(By Rob Christensen, rob.christensen@newsobserver.com) Democratic Senate candidates Elaine Marshall and Cal Cunningham are scrambling in the final days before Tuesday's primary runoff to find the elusive voter in an increasingly bruising contest that is fraying tempers.In campaign appearances, phone messages and mailings, the hopefuls have argued about who is "a real Democrat," who is a product of the Washington establishment and who has the energy and ideals to carry the fight against Republican Sen.