All 435 seats in the US House of Representatives and one-third of the Senate will be contested in November's elections. Midterm contests are traditionally a stern test for the party that holds the White House, which historically tends to lose congressional seats in these elections, and control of both chambers this time will determine whether President Trump can advance his legislative agenda in the second half of his term. Republican and Democratic candidates have spent the year competing in the primary process, which is now drawing to a close, with primaries held across the country for gubernatorial, Senate and House contests. Following the August 18 primaries, polling showed the Democrats with a six-point lead.

The Democratic Party has also been buoyed by data earlier in the month from a Reuters/Ipsos poll which revealed, for the first time in nearly a decade, that voters prefer the party's approach to the economy. The finding is notable because Republicans have long held the advantage on economic issues in voter surveys, making the shift a potentially significant marker in the campaign. That could prove decisive on election day, November 3.

Elaine Kamarck, a senior fellow at the Brookings Institution, a thinktank, has argued that in America's bitterly divided political climate — "where more congressional districts than ever before are considered 'safe' for one party or the other, real change plays out in congressional primaries".

Results from the August 18 primaries in Florida, Alaska and Wyoming have underlined the shifts now underway in voting preferences among both Republican and Democratic supporters.

Progressive outsiders gain ground

On the Democratic side, a developing trend shows candidates on the party's left defeating centrist hopefuls. In Florida, democratic socialist Angie Nixon defeated her moderate opponent, Alex Vindman.

The result was striking for two reasons. First, the contrast in campaign spending: Nixon raised US$975,000 (£716,000) compared with Vindman's war chest of more than US$16.3 million. Second, Nixon's robust position on Israel — she advocated stripping the country of US aid, a stance that is politically risky in a state home to America's third-largest Jewish population.

The pattern was not uniform. Other candidates backed by the Democratic Socialists of America (DSA) lost to more established Democratic figures. But Nixon's victory added another progressive outsider to November's ballot, echoing outcomes already seen in states such as Wisconsin, Minnesota and Michigan. DSA figures have tapped into significant frustration within the Democratic voter base, which has grown increasingly vexed by cost-of-living pressures and increasingly discontented with the party establishment.

Trump ticket no longer golden

Democrats are growing more optimistic about retaking control of the US Senate in November, a task that would require a net gain of four seats — a high bar, given that most Senate seats up this cycle are defended by incumbents of one party or the other.

An emerging trend from recent Republican results suggests the once highly sought-after Trump endorsement is no longer the guarantee of victory it once was. The president's first choice in Florida's 19th congressional district, Catalina Lauf, lost to Jim Schwartzel. Similarly, in Wyoming's Republican primary for governor, sitting state senator Eric Barlow defeated the Trump-backed Megan Degenfelder.

In South Carolina, Darline Graham — who replaced her brother Lindsey Graham as senator when he died in July — won a run-off primary with strong backing from the president. But given the late senator's prominent profile, she is perhaps best seen as a continuity candidate whose victory rested on name recognition as much as on the Trump endorsement.

Defiance of the 47th president among registered Republican voters appears increasingly common, with the president's preferred candidates in the Iowa, Georgia and South Carolina gubernatorial races all losing.

Trump's job approval ratings remain in negative territory. A recent RealClearPolitics polling average put the president's approval at 39.2%, with 58.4% of respondents saying they disapprove of his performance.

The war in Iran is having a daily impact on the lives of ordinary Americans through rising fuel prices, and the survey found that just three in ten voters approve of Trump's management of the conflict. This may help explain why some Republican voters are prepared to reject the president's endorsement.

Rural voters turn away

Rural voters are emerging as a key demographic apparently turning away from Trump. Sharp rises in fuel and fertiliser costs are hitting grain producers particularly hard, while the president's tariff regime is hurting agricultural exports. Rural counties have been a cornerstone of Republican electoral strength in recent cycles, which is why even softening enthusiasm in these areas matters to GOP strategists.

A Fox News analysis found that among rural voters, Trump's net job approval fell from +20 in early 2025 to -14 in May 2026. A recent article by Brookings senior fellow William A. Galston noted that Trump carried 64% of the rural vote to Kamala Harris's 34% in 2024. Galston believes that in November, while Republican voters may not cross over to Democratic candidates, there is a strong possibility more will simply choose not to vote at all.

Further bad news for Republicans came in a Pew Research study from July, which found that — despite Trump himself not being on the ballot — nearly twice as many voters, 42%, will use their ballot to vote against him as will use it to vote for him.

Redistricting clouds the picture

All might not be lost for the GOP, however. It may look as though the Democrats are on course to retake the House — and potentially also the Senate — in November, but the impact of significant redistricting by various states, under the administration of both parties, has yet to be seen.

Redistricting is the process by which a state redraws the boundaries of its electoral seats to better reflect its demographics. It happens automatically every ten years, but a number of states have redrawn their boundaries since July 2025 outside this automatic process. Analysis shows that of the ten states that engaged in voluntary redistricting, the new electoral maps of eight favour Republicans.

So while Democrats hold a clear polling edge and obvious momentum, the outcome of the midterms remains far from certain — and with it, the balance of power in Washington for the remainder of the president's term.

Richard Hargy, Lecturer in International Studies and Politics, Ulster University; Queen's University Belfast. This article is republished from The Conversation under a Creative Commons license.