US midterm elections under way as battle for Congress turns on battleground seats

The US has been voting for senators, members of the House of Representatives and state governors in the midterm elections, in a vote seen as a referendum on President Donald Trump's agenda that will shape the rest of his presidency.

Most US election seats are reliably won by one party, so control of Congress comes down to a few competitive battleground seats. Experts track these to predict overall results; if a party wins seats they were expected to lose, it often signals a successful night.

Before the election, the Cook Report classified seven Senate races as genuine tossups. The Democrats need to win at least four of these, alongside the other races they are expected to win.

Democrats are now favoured in enough House seats to take the chamber without winning any of the 18 seats the Cook Political Report classes as tossups. If they win every seat they are expected to win, they will comfortably win a majority.

The balance of power now turns on whether Democrats hold the 18 seats rated lean Democratic. Republicans, favoured in 195 seats, would need to sweep all 18 tossups and flip five Democratic-leaning seats to win.

Republicans are defending a majority in the 435-member House. Democrats hold 212 House seats and need 218 to win control. Members of the House serve two-year terms and face re-election every even year.

Thirty-three of the 100 members of the upper chamber, the Senate, are being elected regularly this year, along with two other special elections. Republicans had the Senate majority before the election. Senators serve six-year terms.

Gubernatorial elections are taking place in 36 states, as well as three territories. Republicans and Democrats held 18 of these state governorships each before the election. Three incumbent governors are retiring.

The US legislature, Congress, has two chambers: the House of Representatives and the Senate. The House has 435 voting seats, each representing a district of roughly similar size, with elections for each seat every two years.

The Senate has 100 members who sit for six-year terms, with one-third of the seats coming up for election in each two-year cycle. Each state has two senators regardless of population, meaning Wyoming, with fewer than 600,000 people, carries the same weight as California, with almost 40 million.

In most states, the candidate with the most votes on election day wins the seat. However, Georgia and Louisiana require the winning candidate to garner 50% of votes cast; if no one does, they hold a runoff election between the top two candidates.

Maine and Alaska use ranked-choice voting as opposed to first past the post in congressional elections. Voters rank candidates in order of preference; if no candidate receives a majority of first-choice votes, the least-supported candidate is eliminated and their ballots are transferred to each voter's next-ranked candidate until a candidate wins a majority.

Florida and Ohio are having special elections for the Senate because the previous holders of their seats, Marco Rubio and JD Vance, resigned to join the executive branch following the 2024 presidential election.

The election results are reported by the Associated Press. AP will call the winner in a state when it determines the trailing candidate has no path to victory, which can happen before 100% of votes in a state have been counted.