Polls Point to a Good Night for Democrats, but Voting History Says Forecasts Cannot Be Trusted

The Democratic Party heads into the pivotal US midterm elections with high expectations, but the history of polling misses is a reminder that last-minute deciders and sampling problems mean there is no guarantee those expectations will be met.

A historically unpopular Republican president, an American public unhappy with the rising costs of food and bills, and months of favourable polls all point to a good night for the Democrats on Tuesday, the report said.

The polls suggest Democratic candidates lead in well over the 218 seats needed to flip control of the House of Representatives, the lower chamber of Congress, and that they are tied or narrowly ahead in the key Senate races.

A recent New York Times poll put the Senate race in South Carolina level, a state Donald Trump won by 18 percentage points in 2024. Recent CNN surveys put the Democrats ahead in Texas, Kansas and Maine.

Recent US political history, however, is littered with examples of polls that were off the mark even days before an election. Trump outperformed predictions on his way to White House victories in 2016 and 2024, and his narrow defeat in 2020 came after most surveys had indicated a more comfortable win for Democrat Joe Biden.

This year's primaries produced big surprises of their own. In Michigan's Democratic Senate primary, polls suggested Abdul El-Sayed was poised for a double-digit win; the final margin was 1 percent. In Wisconsin's Democratic primary for governor, a candidate whose polling lead approached 20 points lost by a fraction of a percent.

Clifford Young, president of Ipsos Public Affairs, which conducts political and market research surveys, said polling has become difficult in recent years because it is harder to reach Americans as they abandon landlines and screen their calls, and many of those who are reached have become less willing to participate.

"Conservatives, especially those on the far right, are much more anti-establishment by nature," Young said. "And they don't participate in anything. They hate the system. That's the challenge." If Republican voters are systematically undercounted and polling companies do not take that into account when building their voting models, he said, the data could skew towards the Democrats.

One explanation for Trump's overperformance in previous presidential elections is that his supporters, many of them not regular voters, turned out in higher-than-expected numbers. That unpredictability is a main factor behind the notable recent polling misses, even though the margins in most reputable polls were off by only a few percentage points.

In a close race, those few points can make the difference between victory and defeat, and this year many of the key Senate races sit within those narrow margins.

Midterm general election polls have in recent years proved more accurate, in part because Trump, and his unique ability to draw disaffected Americans to the polls, was not on the ballot. In 2022 they suggested Democrats would avoid an electoral wipeout despite President Biden's low approval numbers; the party lost control of the House, but the margins were slim and Democrats kept control of the Senate.

Young said nominating contests have historically been volatile, with voters more likely to make up their minds at the last minute, so this year's primary surprises should not be read as a sign that the current general election polls are off the mark.

It is common for the president's party to have a bad night in the midterms. In 2010 Republicans flipped more than 60 House seats and made gains in the Senate, against the backdrop of an economy struggling to recover from the financial crash and conservative fears over President Barack Obama's healthcare reforms; a defeat had been predicted by the polls, but not on that scale.

The roles are reversed this time, with the Democrats in opposition and the economy on voters' minds, but there are reasons Democrats may not do as well as history or Trump's low approval rating might suggest. Much of the territory in play is ground Trump conquered with ease in the presidential election two years ago, a home game for Republicans; changes to House boundaries over the years have meant fewer seats switch parties; and deeper polarisation has left fewer swing voters, in an electorate some experts describe as calcified.

Republicans have also enjoyed a cash advantage that has given them hundreds of millions of dollars to spend on attack ads in the final weeks. Even so, even the kind of polling lean seen in recent presidential elections would suggest Democrats are likely to have a good night on 3 November, and inaccuracies can go both ways: in last year's state and special elections, Democrats outperformed most surveys as their voters turned out in unexpectedly larger numbers. Trump holding final-days rallies in states he won comfortably in 2024 has lifted Democratic hopes that Republican internal polling shows their candidates in trouble. But voters can change their minds right up to election day, and undecided voters can all break the same way. "I think we're doing a better job," Young said. "But part of the problem we always have is not just with the pollsters. Part of it is that we're dealing with humans. Humans are not easy."