Marshall almost lost in 2006 because of low black turnout. That will not be a problem with Obama at the top of the district. Hillary Clinton will bring out those longtime Newt Gingrich style Hillary haters in droves and pull Marshall under.
You are wrong time and again about this. The GOP will define the race as black vs. white. And the majority whites will vote for Marshall's opponent in mass. Obama is a candidate that loses 1/3 of the democrats down here in GA. How does that help down ticket races? When you have Democrats who won't vote for him.