Why does the presidential race appear, at least on the basis of campaign coverage, to be nothing but a succession of gaffes? A week or two will go by without news, and then either President Obama or Mitt Romney will say something damaging, and that comment will define the contours of the debate until the next verbal own goal. … The centrality of the gaffe is an outgrowth of horse race coverage. Political reporters have little interest in informing the public about the policies advocated by the two candidates. Their job is to tell us every day who is winning. And since very little changes in the horse race from day to day, the main device they have to drive the narrative is the gaffe. The gaffe is a candidate saying something unplanned and unwelcome. As campaign reporters define their job, the gaffe is the primary form of ‘news.’
— Jonathan Chait, writing in New York magazine.