Over the weekend, people who pay close attention to political polls received a November surprise: a well-respected poll showing Vice President Kamala Harris leading in Iowa by three percentage points.
Iowa has not been considered a swing state in the presidential race. Former President Donald J. Trump won the state by eight points in 2020, and every other poll there this year has shown him with a lead of at least four points. The Cook Political Report rates Iowa as “solid Republican.”
The new poll was startling, and actually caused some jostling in online prediction markets, in part because of the source: the revered independent pollster J. Ann Selzer, who is one of the most highly rated practitioners in the country and has a track record of exemplary work.
But as I’ve written before, polls are best understood in aggregate, and any single poll by itself is prone to a certain amount of error. Overall, Mr. Trump still has a three-point advantage in The New York Times’s polling average of Iowa, even with the new Selzer poll included.
So why the uproar over this single poll, and what should voters make of it as we head into Election Day?
The poll has caused so many pundits and politicos to sit up because Ms. Selzer has been here before. In the final week before the 2020 election, Ms. Selzer released a poll of Iowa conducted with The Des Moines Register that showed Mr. Trump leading by seven points in the state. It was an outlier; other polls showed a much tighter race, with averages showing Mr. Trump ahead by just over one point. Ms. Selzer’s own poll from September of that year had shown Mr. Trump in a tie with Joe Biden.
