Reporters are used to covering campaign events that do not literally decide the nomination: each new poll, new attack ad, or new fundraising number brings reams of copy and minutes of chatter about how it might change the race, and often, more self-referentially, how it might change the narrative of the race.

This strand of speculative campaign coverage, with its endless dissection of strategy, draws some readers and repels others. But one of the hoary old conceptions of much day-to-day journalism is that it is meant to be a mirror of events, not a shaper of them.

That is clearly not the case when candidacies rise and fall after the tiniest of results are amplified through the campaign press’s churn. (How tiny? Iowa’s delegates represent just 1% of the Tampa vote; the Republican caucus-goers could have fit into a football stadium; even coming in last among the major contesting candidates, Bachmann was no more than 13 delegates out of the lead.)

But voters do look to earlier results to coordinate their choices. The present campaign offers a perfect example, as Republican voters who prefer a candidate besides Romney may now turn to Santorum as the candidate most likely to edge him.

There’s nothing wrong with a certain class of journalists trying to anticipate these shifts. And by doing so, they will inevitably amplify the very phenomenon they seek to describe, as there is no way to report on momentum without also contributing to it.

As last night’s votes trickled in, cable viewers likely heard analyst panels asked variations on this question: “What’s tomorrow’s headline?” Unpack that (somewhat quaint) query’s reflexivity, and it shows that journalists sometimes try to anticipate and cover the changes that their and their colleagues’ coverage will create.

Such discussions are a mixed blessing; they reflect a consciousness of the dynamic, while inevitably playing into it. As Brendan Nyhan argued for CJR just before the caucuses, reporters need to be conscious of the way that they create as much as report on momentum, and straightforward with their audiences that that’s what’s going on. Talking about changes to the narrative, even if it is part of a feedback loop and couched as an exercise in predictive expertise, may be as full a reckoning of journalists role in creating momentum as can be hoped for.

Politics, you may have heard, is a messy business.

Clint Hendler is the managing editor of Mother Jones, and a former deputy editor of CJR.