Iowahawk Guest Opinionby Senator Hillary Clinton (D-NY)From the earliest days of the campaign, the race for the 2008 Democratic presidential nomination has been a hard fought, neck-and-neck struggle. But now, as the race enters its final stretch, it has become increasingly obvious that the eventual outcome is no longer in doubt. With a difficult general election looming, Democrats need to put our family squabbles aside and unite behind the eventual nominee. And so, in the interest of Party unity, and his own health, I am calling on Senator Obama to gracefully accept defeat.First, let me congratulate Senator Obama and his...