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The Democratic Party arrives with great expectations of victory in the mid-term elections in the United States, when a large number of Congressional seats will be up for grabs at the polls.
The low popularity of American President Donald Trump (Republican Party), who has recorded historic rejection rates, Americans' dissatisfaction with rising food prices and household bills and months of favorable polls indicate that the Democrats could perform well in Tuesday's elections (3/11).
According to opinion polls, Democrats are leading the dispute for a number of seats well above the 218 needed to gain control of the Chamber of Representatives, equivalent to the Chamber of Deputies in Brazil. In the main Senate races, Democratic candidates appear tied or with a small advantage over their Republican opponents.
A recent survey by the American newspaper New York Times showed a tie in the Senate race in South Carolina, a state where Trump beat Democrat Kamala Harris by a difference of 18 percentage points in the 2024 presidential race. Recent CNN surveys show Democrats ahead in Texas, Kansas and Maine.
But will the polls be close to the results of the polls?
The recent political history of the United States is full of cases in which voting intention polls showed very different numbers from the polls, even when carried out a few days before the vote. Trump performed better than indicated in the polls by winning the 2016 and 2024 presidential elections. In 2020, Trump lost by a small margin, although most surveys pointed to a more comfortable victory for Democrat Joe Biden.
Earlier this year, polls indicated that Democrat Abdul El-Sayed would win his party's Senate primary in Michigan by at least ten percentage points. But the advantage was only one percentage point. In the Democratic primary for governor of Wisconsin, the candidate who led the polls by almost 20 percentage points ended up defeated by a difference of less than one percentage point.
According to Clifford Young, president of Ipsos Public Affairs, a company specializing in opinion and market research, carrying out electoral research has become more difficult in recent years. With the abandonment of landlines and the growing habit of screening calls, it is becoming increasingly difficult to contact Americans. Furthermore, many of the people who answer calls from research institutes are less willing to participate in surveys.
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“Conservatives, especially those on the far right, tend to be much more rejecting of institutions,” says Young. "They don't participate in anything. They hate the system. That's the challenge."
If Republican voters are being systematically underrepresented in polls, and pollsters do not take this into account when developing their vote projection models, poll results could be skewed in favor of Democrats.
This is one of the reasons why it has become more difficult for pollsters to estimate which voters will actually go to the polls.
One of the possible explanations for why Trump exceeded expectations in the previous presidential elections is that his supporters, many of whom were not in the habit of voting, went to the polls in greater numbers than opinion polls indicated.
This unpredictability is one of the main factors behind the most significant controversies in recent electoral polls, although, in most surveys by respected institutes, the difference between projected numbers and actual results was just a few percentage points.
In a close race, a few percentage points can determine a candidate's victory or defeat. And this year, many of the top U.S. Senate races are in that narrow range in the polls.
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In recent years, polls for the midterm general elections have been closer to the outcome of the polls in part because Trump, with his unusual ability to mobilize disaffected American voters to vote, was not among the candidates.
In 2022, when Biden was president, polls indicated that Democrats would defy expectations and avoid a crushing defeat in the midterm elections, despite Biden's low popularity.
Although the Democratic Party lost control of the House of Representatives, the difference in seats was small, and the Democrats maintained their majority in the US Senate.
Although the results of this year's party caucuses brought bigger surprises, Young says that these contests have always been unpredictable, as many voters decide who to vote for only at the last minute. Therefore, these results should not be seen as a sign that the current general election polls are wrong.
It is common for the president's party to perform poorly in midterm elections.
One of the most striking examples in recent years occurred in 2010, when Republicans won more than 60 seats in the House of Representatives that previously belonged to Democrats and expanded their representation in the Senate.
At the time, the economy was still facing difficulties in recovering from the financial crisis, and conservative Republicans were concerned about the healthcare reform proposed by then President Barack Obama (Democratic Party). Polls already pointed to a defeat for the Democrats, but not on that scale.
In 2026, the situation was reversed: Democrats are in opposition, and the economy is once again one of voters' main concerns. Still, there are several reasons why the party may not perform as well as the record of these elections would indicate or as some expect given Trump's low popularity.
Firstly, most of the regions where there will be important disputes in this election gave Trump a comfortable victory in the presidential election just two years ago. These are territories where Republicans have an electoral advantage.
Additionally, changes made over the years to the geographic boundaries of House of Representatives electoral districts have reduced the number of seats that typically change party at each election.
In other words, imagine that the majority of voters in district A vote for candidate 1, but in other elections have already elected candidate 2, and that the majority of district B votes for candidate 3, but has also already elected candidate 4. Electoral redesign (called gerrymandering in English) swaps districts A and B for districts in C and D in such a way that both have regions where a large majority of voters live who always vote for candidates 1 and 3. Thus, people who usually Voting for candidates 2 and 4 becomes a small majority, preventing districts from switching parties at each election (so-called pendulums).
Another factor is the increase in political polarization, which has reduced the number of voters willing to change their party preference. According to some experts, voters' choices are increasingly consolidated.
Republicans also have a financial advantage, which has allowed them to allocate hundreds of millions of dollars to running advertisements against their opponents in the final weeks of the campaign.
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The statistical models used in electoral research seek to monitor changes in the factors that influence the outcome of the elections. A well-designed survey must also take into account possible problems that could compromise the reliability of the data.
Every survey has a margin of error, which represents the degree of statistical uncertainty calculated based on the sample size in relation to the population as a whole. Therefore, averaging the results of several surveys can offer a more accurate prediction than an isolated survey.
Right now, even though the polls show skews similar to those seen in the last presidential election, the numbers still indicate that the Democrats could do well on 11/3. Furthermore, poll errors can favor either party. In last year's state and special elections, Democrats had better results than most surveys indicated, because their voters turned out to the polls in greater numbers than expected.
The fact that Trump held rallies in the final days of the campaign in states where he won handily in 2024 must have raised Democrats' hopes that internal Republican polls are pointing to difficulties for conservative candidates.
Still, voters can change their minds until the last minute — and sometimes last-minute changes can alter the course of a race.
In other cases, undecided voters, who still represent an important portion of the electorate in many of these elections, end up opting for the same candidate or party they have already voted for before.
Election polls will always have some degree of uncertainty. Knowing how to deal with this unpredictability requires both scientific knowledge and experience.
“I think we’re doing a better job,” says Young. "But part of the problem we always face is not just in research institutes. We also have to deal with human beings. And human beings are complicated."
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