What The Midterm Senate Polls Won’t Tell You (And Where They Might Be Wrong)

With the midterm election fast approaching, there’s a great deal of speculation about the accuracy of the polls. Democrats are generally hoping that the polling is right, as it suggests they are poised to take control not only of the House of Representatives but probably also the Senate. Correspondingly, Republicans are hoping the polls are wrong. They speculate that conservatives are more distrusting of pollsters and therefore less apt to respond to their inquiries, and that the polls aren’t adequately adjusting for this.

There is no way to know for sure whose hopes are more realistic. At the same time, we aren’t flying completely blind. We now have a track record of Senate polling across five prior federal elections in the Donald Trump era. If we assume that polls will perform as they have typically performed on a state-by-state basis throughout this era, what would that mean for this election?

The 13 states whose 2026 Senate races are generally thought to be the most competitive have each already had at least three Senate elections during the Trump era (from 2016 to 2024). If we take how the two parties’ Senate candidates fared in the final RealClearPolitics (RCP) average of recent polling in those races and compare that with how they fared in the final results, we can see whether polling underestimated one party or another in a given state — and by how much.

Take New Hampshire, for example. In 2022, the RCP average suggested that Democrat Maggie Hassan would win by 1.4 percentage points over Republican Don Bolduc in their Senate race. Hassan actually won by 9.1 points, so the polls underestimated her — and hence the Democrats — by 7.7 points in that race. In 2020, there wasn’t enough Senate polling in New Hampshire to generate an RCP average, but the six polls taken entirely in October or November underestimated the Democrats’ margin of victory by an average of 0.9 points. In 2016 Senate polling, the RCP average underestimated the Democrats’ final winning margin by 1.7 points. So, across the Trump era, polls have undersold the Democrats by an average of 3.4 points per year in Senate elections in the Granite State.