On Face the Nation, Sen. Lindsey Graham just said "we've seen a tightening of the race [and] I really believe Obama is the virtual incumbent and if he's not at 50 percent in North Carolina he's not going to win."
I'm open to the idea -- actually I believe that undecideds will break disproportionately for McCain. I would say it's become conventional wisdom, though I have yet to see any solid evidence, as opposed to informed speculation, for why that should be the case. I would say I believe it as a matter of caution as much as anything.
But in an election in which 1) the incumbent Republican president is running under 30% approval and 2) most voters believe McCain would be a continuation of the Bush presidency, to say that Obama is the "virtual incumbent" is a bit of a stretch.