See Rassmussenreports.com balance of power calculator.
McCain will have to hold on to all of Dubya's 2004 states including NV, OH, and VA and take one of CO., IA, or NM back to Red, or switch a Kerry state like MN 11(Pawlenty) or MI 17(Romney).
If he takes NV, OH, VA, and NH (4), but loses CO, IA, and NM it winds up a 269-269 tie.
I think that leads us dangerously close to a bad situation that will make 2000 look like a walk in the park.
So Obama does not have 273, but 267 as of now.