American opinion polls show the Democrats' lead, despite doubts about their reliability

Successive opinion polls show a noticeable lead for Democrats over Republicans ahead of the midterm elections for the US Congress, scheduled for next month, which reinforces expectations of a blue electoral wave, despite some Republicans questioning the accuracy of these indicators and the possibility of them exaggerating the size of the Democratic lead.

According to a report published by Axios, any limited error in the opinion polls may determine whether Republicans will maintain control of Congress, or whether President Donald Trump will face a Democratic majority in the House of Representatives and the Senate.

In the House of Representatives, Democrats lead by 49.8% compared to 41.9% for Republicans, according to the Real Clear Politics poll average. The Cook Political Report expects Democrats to achieve gains ranging between nine and 19 seats, which may be enough to regain a narrow majority.

As for the Senate, the report expects the Democrats to achieve net gains ranging between two and six seats, while the party needs four additional seats to control the Senate.

Opinion polls also reflect a decline in Trump's popularity; The approval rate for his performance is 37.6% according to the Cook Index, while a poll conducted by The Economist and YouGov magazine showed that 35% approve of his performance, compared to 60% who disapprove of it.

A problem in measuring voters

But these numbers are not without doubts. Opinion polls failed to estimate the extent of support for Trump during the 2016, 2020, and 2024 elections, and research indicates that Republicans are relatively less likely than Democrats to participate in telephone polls, in conjunction with a general decline in response rates since the late 1990s.

Brent Buchanan, a Republican pollster and founder of Signal, said the surveys receive more responses from voters who voted for former Vice President Kamala Harris than from voters who voted for Trump, but he noted that professional institutions can reach the least responsive groups.

Polling organizations adjust sampling weights to reflect the demographics of Republican voters, but this treatment can lead to misleading results if Republicans who are willing to participate in surveys are more likely to vote Democratic than those who do not, according to Matthew Tyler, an assistant professor of political science at Rice University.

Also, YouGov results showed that the Democrats' lead ranged between six and 16 percentage points in a September poll, depending on the criteria used to determine voters likely to participate.

The foundation's chief scientist, Douglas Rivers, described the 16-point difference as likely greatly exaggerated.

Despite these reservations, most pollsters believe that Democrats have an advantage before Election Day.

Buchanan sums up the Republican position by saying that pinning hopes that the polls are wrong is "not a solid basis."