You can usually tell how successful a campaign is going to be by the coherence and consistency of its message, its rhetoric, what the candidate and campaign say each day. Campaigns are constantly fine-tuning this - the trail is just one long focus group, and you can tell what’s working and what’s not pretty easily. The more consistent the message, and the more coherent it is - in other words, the way everything (speeches, issue briefs, press releases, ads, imagery) fits together, pointing back to a few clear, central points - the more successful the candidate is going to be. This is Obama, at least so far.
You can also tell a candidate is having trouble when his message does not cohere, either because s/he cannot put the relevant ideas together into a coherent package, or because people don’t like what they hear, necessitating constant changes in an attempt to find something that resonates. This describes McCain (also, so far) whose speech last night wandered all over the place (he’s not seeking a third Bush term, Obama is inexperienced, the world is dangerous, McCain wants to reform government, etc.)
George H.W. Bush, interestingly, is the best exemplar of both message discipline and message entropy in recent political history. In 1988, he began pounding Michael Dukakis as a wacky liberal in June and kept on the same points until November. But four years later, he couldn’t make up his mind what was worst about Clinton - whether he was inexperienced, had done a terrible job in Arkansas, was corrupt, had avoided serving in Vietnam, or had protested the war “in a foreign land” (Britain). His attempts to portray himself as dependable leader (”the man behind the desk”) seemed similarly out of sync in the economic doldrums of that year.
