Here in New Hampshire, for instance, local TV heavyweight WMUR and the Concord Monitor are already anticipating the “Santorum surge” foreshadowed by a recent Des Moines Register poll, which placed Romney first, Ron Paul second, and Rick Santorum third. A third-place Santorum finish is likely to generate a wave of positive coverage about his “momentum” even though there is little indication that the former Pennsylvania senator has the financial or organizational capacity or the broad base of party support necessary to compete nationally with Romney (as Ezra Klein notes, Intrade puts his chances at 4%). Likewise, if Romney is edged out for first place by Paul or Santorum, the resulting coverage will almost surely overhype the result as signifying a more general weakness of his campaign despite the likely eventual outcome of the race.

The result in Iowa is genuinely significant because of the weight it is given by party actors, but journalists should recognize that “momentum” is a subjective interpretation of the results that they help to create. Reporters in New Hampshire and other early states ought to think carefully about how to select and frame their post-Iowa stories rather than passively accepting the conventional wisdom about the state of the race.

Brendan Nyhan is an assistant professor of government at Dartmouth College. He blogs at brendan-nyhan.com and tweets @BrendanNyhan.