This is another node whose title might need a bit of explanation. In political campaigning for elections, there are two major types of theories about what makes a successful campaign. One explains the campaign through "macro" explanations, while the other explains it through "micro" explanations.
The "Macro" explanation says that the candidate and campaign are not very important, but that the election will instead be decided by things like overall economic conditions, the demographics of the electorate, and "waves" of political sentiment. Researchers or pundits who believe in this theory try to find the best economic indicators or demographic trends that will determine the election.
On the other hand "Micro" theory focuses on the candidate and the campaign staff, and their strategic and tactical decisions. They look at such things as whether the candidate is charismatic and well-spoken, whether the campaign staff are experienced and working well together, and the decisions made in electoral college strategy.
As we get into campaign season, the race between Barack Obama and Mitt Romney will be one of the top stories in the media, and everyone from pundits to your annoying brother-in-law will be mansplaining what is "really going on". Variations on macro and micro explanations for the result of the election will be handed out self-assuredly.
My own belief, as with so much in life, is that the answer is somewhere in-between. The amount of presidential elections in the modern era (considered to be post-World War II in this context) is small enough, and has involved enough outlying data, that its hard to model what a standard election would look like. But there is a number of years where the election could be reasonably explained in terms of one or the other. Was 1964 about the electorates differences with Barry Goldwater's politics, or an emotional response to the death of John F Kennedy? Was 1976 a referendum on inflation and other economic conditions, or was it about Gerald Ford's personal qualities? Was George Bush's defeat in 1992 about the recession, or did Bill Clinton win because of the efficiency of his campaign team? Arguments and explanations about this can go on forever, but very few have predictive power.
The reason we have elections in a democracy is because we don't know the results. There is always some uncertainty about what will happen, and no one knows what the deciding factor is. It may be that elections are decided by whether some arcane economic variable shifting a fraction of a percent, or by a candidate appearing on the cover of Rolling Stone wearing pants that are a bit too tight. But I don't believe that we will ever know what the "real" explanation is for why a campaign succeeds or fails.