.. in chess is that you get to see what the opponents move is before committing to a strategy. Thus when the Democrats selected Joe Biden for VP nomination, this opened up the current strategy of the Republicans to fill a vacant niche of "woman on a presidential ticket". I think the Republicans looked several moves ahead on this one, and the current Republican plan bears no resemblance to that which would have been the case had Hillary been the VP nominee (see p-K4 vs p-Q4).
Stringing another "West Wing" analogy, I think the best chance for Obama is for McCain to have been a well known supporter of [big oil] energy (don't know? is he?) - and for there to be a big [oil installation] scary incident at a crucial stage in the election campaign.