Why Democrats’ Red-State Leads Might Not Be What They Seem

With just one day until Election Day, Democrats are highly favored to retake the House and could gain control of the Senate, depending on how you interpret the polls and whether you believe they accurately reflect public opinion. Republicans believe the polls underestimate them, while Democrats seem nervous that the GOP might be right. To take back the upper chamber, however, they’ll need to win key battlegrounds in red states. Polls show Democrats with slim leads in most, well within the margin of error, but are those margins real or a miscalculation?

Democrats and Polling Misses

Republicans have complained for years that the polls overcount Democrats and undercount Republicans, and they’re not wrong. But the issue is more nuanced. Yes, polls underestimated Trump’s support in the last three presidential elections, with Senate polls overstating Democrats by “roughly 3.5 to 5 points nationally,” according to FiftyPlusOne. If this year’s polls miss the same way, Democrats could see their road to a majority veer off a cliff. Republicans would gain leads in Alaska, Iowa, Kansas, Maine, and Ohio and pad their advantages in Nebraska and South Carolina. Democrats would still have a comfortable lead in North Carolina but would be neck-and-neck in Texas and would likely fall behind in Michigan, putting them three or four seats short of a majority.

The most common explanation is nonresponse bias, meaning the polls could be off because Trump supporters are less likely to answer surveys. However, over the years, many pollsters have begun weighting their samples to compensate for nonresponse bias. So if a survey lacks Republicans, pollsters give more weight to the Republicans who took the poll. This method isn’t 100% accurate, but it can limit how far off the polls are.

Midterm polls, though, haven’t followed the same pattern. In 2018, for instance, polls overestimated Democratic candidates in 18 states and Republican candidates in 12, and the results were also mixed in 2022, according to a New York Times analysis. If the polls miss as they did in those two midterm cycles, Democrats could win nearly every Senate seat they’re leading in today. Their margins would grow to about 5 points in Maine and Texas, while Iowa and Ohio would be essentially tied and Michigan would be up for grabs. Then again, these estimates don’t yet reflect Sunday’s news that Democratic Rep. Haley Stevens, who narrowly lost the party’s Senate primary to Abdul El-Sayed in Michigan, broke ranks and endorsed Republican Mike Rogers. Ultimately, you never know which way the margin of error will swing. Just because polls didn’t consistently underestimate Republicans in the last two midterms doesn’t mean they won’t this year.

Hide and Seek

The Economist recently found that “the more a state leans towards one party, the more the polls have underestimated it, by an average of 1.6 points for every ten points of vote share. The reason for this is unclear, but the pattern is apparent across all elections since 1998.” This matters very little in places like Massachusetts, but in the current race for the Senate, most battlegrounds are in Republican territory. So “if surveys are underestimating red-state Republicans by one to two percentage points in states where Democrats lead polling averages by just 1.5 points,” explained The Economist, “the error could be enough to tilt the balance and thus the Senate.”

The polling team at State Navigate ran into some issues last month that could point to such an error. At the beginning of October, it highlighted two problems in its Iowa survey in State Senate District 35: “1. There are more likely Trump voters who are lying about their 2024 vote for the President than anywhere else we’ve polled, and 2. Even accounting for this, rural Republicans in Iowa are difficult to reach.” Pollster Patrick Ruffini at Echelon Insights pointed out a similar issue on X, posting a map of where Republican voters have been the hardest to reach; many of those places were key battlegrounds in red terrain. Still, some of those Trump voters who won’t admit their 2024 vote may be unhappy enough with the administration to stay home, which would shrink the error.

When it’s all said and done, though, undecided voters will likely sway the overall outcome. According to Strength In Numbers, Trump voters outnumber Harris voters nearly 2 to 1 among undecideds. Notably, however, late deciders broke against the president’s party by a ten-point margin in 2022.

While polls will inherently have some errors, predicting which direction they will swing is nearly impossible. If the polls overstate Democrats, it will look like the same old story and perhaps further erode public trust in polls. If they understate them, Democrats could get their blue wave. Either way, a miss of just a few points in a handful of red states might be enough to decide who controls the Senate.