What kind of a historian is Douglas Brinkley anyway? These days Brinkley is acting a lot less like a historian and a lot more like a PR flack for John Kerry, the subject of Brinkley's flattering bestseller "Tour of Duty: John Kerry and the Vietnam War." Brinkley proclaims his independence from the Kerry campaign -- "This is my book, not his," he writes in "Tour" -- but he's become a major player in the Kerry agitprop machine.