What are the races to watch in the US midterm elections and why do they matter?

Donald Trump will still be US president on the morning of 4 November. But he could be facing a very different political landscape, depending on the results of the US midterm elections held the previous day.

As the name implies, midterm elections fall nearly halfway through a president’s term. They are often a telling referendum on the sitting president’s performance, something Trump is actively encouraging by telling voters “pretend I’m on the ballot”. In this case, voters will decide whether Trump’s Republican party can retain its grip on Congress.

Democrats are hoping to capitalise on growing discontent with Trump to seize control of the US House of Representatives, and possibly the Senate. Republicans are fighting to preserve their congressional majorities and prevent a fresh period of legislative paralysis and investigations into the White House.

What is being decided?

The US Congress in Washington has two chambers: the House of Representatives and the Senate. Both must approve federal legislation before it can become law and both play important roles in overseeing the executive branch.

The House is elected every two years, meaning all 435 voting seats are contested at every congressional election. The Senate has 100 members serving staggered six-year terms, so roughly a third of its seats are up for election every two years.

This year’s ballot includes:

• All 435 seats in the House of Representatives. Republicans are defending a narrow majority, with Democrats needing a net gain of four seats to take control.

• 35 seats in the Senate. Thirty-three seats are up in regular elections, along with two special elections in Florida and Ohio to fill the remainder of terms that were vacated early. Republicans currently hold 53 seats, against 47 held by Democrats and independents who caucus with them. Democrats need to gain four seats to secure a majority.

• 39 governorships. Voters will choose governors in 36 states and three US territories.

• Thousands of state legislative seats, as well as local offices, judicial contests and ballot measures on issues including taxes, abortion rights and voting rules.

The elections for Congress will determine which party controls Congress for the final two years of Trump’s second term. The governorships and state legislative contests will shape policymaking closer to home, from education and reproductive rights to taxation and the administration of elections.

Why do the midterms matter?

They have a long history of punishing the occupant of the White House. The president’s party has lost House seats in 18 of the past 20 midterm elections, a 90% rate of loss that stretches back to 1946.

The pattern is not inevitable. George W Bush’s Republicans gained seats in the 2002 midterms, following the September 11 attacks. But Barack Obama’s Democrats suffered a “shellacking” in 2010 and Trump’s Republicans lost the House in 2018.

Republicans enter this election with a narrow margin for error in the House and a more substantial advantage in the Senate. The RealClearPolitics average of national generic polls showed Democrats leading Republicans by 8.2 points in early October. Trump has been forced to hold campaign rallies in what should be safe Republican states.

But political polarisation and years of redistricting have reduced the number of genuinely competitive House districts, making it harder for either party to translate a national swing into a big change in seats. The Reuters news agency has estimated that only about 40 to 50 House races are truly competitive.

What are the races to watch?

Several Senate contests have emerged as key battlegrounds. In Michigan, progressive Abdul El-Sayed is seeking to hold an open seat for Democrats after Gary Peters, the incumbent senator, decided not to seek re-election. In Georgia, Jon Ossoff, a Democratic senator, enjoys a healthy poll lead over Republican challenger Mike Collins.

In Maine, a state won by Democrat Kamala Harris in 2024, Susan Collins, the Republican senator, is defending her seat against Democrat Troy Jackson. Ohio offers another major test, with Democrat Sherrod Brown seeking to return to the Senate against Republican Jon Husted.

Texas has become especially closely watched. Democrat James Talarico is taking on Republican Ken Paxton, the state’s attorney general. Republicans have spent about $210m to help the scandal-plagued Paxton. No Democrat has won a statewide election in Texas since 1994. Trump won Texas by nearly 14 points in 2024.

Other contests in Alaska, Kansas, Iowa, North Carolina and New Hampshire could help determine which party controls the chamber (if there is a 50-50 split, JD Vance, the vice-president, a Republican, wields the tiebreaker vote). Latest polls show Democrats ahead in Maine, North Carolina and Kansas, and competitive in Alaska and Ohio.

In the House, the contest is spread across dozens of districts. Republicans are defending vulnerable seats in places including New York, Texas and Iowa, while Democrats are also fighting to protect members in districts made more difficult by redrawn congressional boundaries. Notable gubernatorial elections include Alaska, Iowa, Florida, Georgia, Ohio and Texas.

What are the main issues?

The cost of living regularly tops opinion polls. Democrats are campaigning hard on affordability related to food prices, housing, fuel and healthcare. The war in Iran has added a further complication for Republicans.

Immigration remains another defining issue, with polls suggesting that many voters feel Immigration and Customs Enforcement’s (ICE) hardline approach has gone too far. This could wipe out many of the gains that Trump made with Latino voters in 2024.

Datacentres, AI, tariffs, trade, abortion rights, voting rules and the future of democracy also remain important themes. Democratic socialists scored some notable victories in Democratic primaries, creating momentum on the left of the party.

But in closely fought races, personal credibility, local connections, the ability to appeal to independent voters and a blitz of TV advertising can outweigh the national party message.

Will the elections be free and fair?

The integrity of the midterms is under scrutiny, with concerns ranging from voter registration to the certification of results. Trump has sought to amplify these fears, putting forward a litany of misleading and false claims about threats to US elections.

The justice department has sued states for access to their unredacted voter rolls, seeking to cross-check them against a federal immigration database in an effort to identify ineligible voters. A federal judge ruled that the department’s policy was unlawful, citing limits on its authority and the risks of inaccurate data.

There are also concerns about the use of immigration-enforcement data in voter-fraud investigations, the administration’s efforts to change mail-voting rules and the prospect of federal election monitors at polling places. The NAACP has sued over the planned deployment of monitors, arguing that their presence could intimidate voters.

The risks do not end when polling stations close. Voting-rights advocates are also watching for pressure on local officials to certify results, mass challenges to ballots and legal disputes that could delay or undermine the transition of power.

What happens if Democrats win?

A Democratic victory in either chamber would significantly constrain Trump’s ability to advance his domestic agenda and hasten the president’s decline into “lame duck” status.

If Democrats take the House, Republicans would lose their ability to pass legislation through that chamber without Democratic support. A Democratic majority could launch investigations into the administration, demand documents and testimony, and subject senior officials to sustained congressional scrutiny. They might come under pressure from their support base to impeach Trump.

The Senate confirms cabinet officials, ambassadors and federal judges, including supreme court nominees. A Democratic majority could block or delay many of Trump’s appointments, and force the White House to negotiate over legislation.

Even if Republicans retain one or both chambers, a reduced majority could make governing more difficult, particularly when legislation requires near-unanimous support from the party’s own members.

Why do state elections matter?

Governors and state legislatures have influence over abortion access, education, taxation and voting procedures. State legislatures also play a central role in drawing congressional district boundaries, although the precise arrangements vary by state and some maps are subject to court challenges or independent commissions.

Voting rules are another source of contention. New restrictions on identification, registration and mail-in voting have taken effect in several Republican-controlled states. Supporters describe such measures as safeguards for election integrity; critics argue that they risk making it harder for eligible citizens to vote.

These disputes are especially significant in a political climate in which Trump has repeatedly questioned election procedures and the legitimacy of results he dislikes.

When will we know who has won?

Voting takes place on Tuesday 3 November, but the results may not be known that night. Close contests, different state rules for counting early and postal ballots, and possible recounts or legal challenges could delay the final outcome.

Once the dust has settled, there will be no respite in this – the land of the endless campaign. Attention will soon turn to the 2028 presidential election campaign, when both parties will seek to turn the results of this November into a foundation for the next fight for the White House.