During the last week of the midterm campaign (not counting runoffs, of course), you will hear more and more about which party has “momentum.” Indeed, a big Washington Post headline yesterday read: “Midterm Momentum Belongs to GOP.”
But as Nate Silver and Harry Enten of FiveThirtyEight explained today, polling “momentum” is usually an illusion because it means projecting current trends into the future without particular evidence to support that action. There have been multiple occasions in this election cycle when apparent trends in particular states were reversed overnight.
What the Post poll on which the article linked to above really indicated was a measurement of the national state of play that was in important respects at odds with state-by-state polling. So it wasn’t that big a stretch to predict that the latter would converge with the former between now and next Tuesday, thus creating a sense of “momentum.” But as Silver and Enten point out, that poll was contradicted by a Fox News survey that came out the same day showing Democrats with a generic ballot advantage. So one analyst’s “sign of momentum” could be another’s “outlier” or “noise.” We’ll just have to wait and see.