Where the US midterm elections will be won and lost

Americans head to the polls on 3 November to decide how the rest of Donald Trump's presidency will play out. Thousands of races are taking place across the US, at different levels of government. But the main event for voters will be electing members of the House of Representatives and the Senate, the two chambers that make up Congress. Both of them are currently controlled by the Republicans, the president's party. The success or failure of Trump's final two years in office could rest on the outcome. Here's our visual guide to where the battle for power will be won and lost - from approval ratings, to key races and issues and the huge amount of money being spent.

One of the reasons the opposition Democrats have a chance to take back Congress is the president's low approval rating, which is a good indicator for how well his party could perform. He began his second term as president with an approval rating of just over 50%, according to polling resource website Silver Bulletin, but it quickly fell into the 40s. It was hovering around 42% when Trump decided to launch air strikes with Israel against Iran at the end of February this year but it fell below 40% shortly afterwards. It is currently sitting at about 37%. Eight years ago, Trump's approval rating was significantly higher at this point in his first term, at 43%. Joe Biden's at the same point in his term was at 40%. In both cases, the sitting president lost control of the House in the midterms but kept hold of the Senate. But Trump's poor ratings help explain why Democrats are hopeful of winning both chambers of Congress and why they are setting their sights on states that Republicans have won consistently in recent years.

The current Republican majority in the House of Representatives, the lower chamber, is as thin as it gets - they have 218 representatives, which is the exact number needed to have control, plus one independent who votes with them. Members of the House serve a two-year term so all 435 seats are up for election in November. But most districts are not considered competitive because the party that holds them has such solid support that there is only one likely winner. The Cook Political Report, which analyses campaigns and elections, suggests that just 21 districts are "toss-ups" that could be won by either party. Of those 21 toss-ups, 16 are currently held by Republicans and five by Democrats. If the Democrats win four of those on top of 29 districts classed as likely or leaning Democratic, they will win the House. Historically, the midterms see a high number of seats changing hands in the House, usually in a protest against the White House. The average number lost by the president's party is 27, according to data going back to 1934. Of those 23 elections, the president's party has only made gains in three.

The Republicans have a slightly stronger hold on the Senate. They hold 53 of the 100 seats while the Democrats have 45 and two independents who also vote with them. Members of the Senate serve staggered six-year terms, meaning only a fraction of seats are contested at any given time. This structure gives the governing party a bit more insulation compared to the House. However, unexpected shifts in voter sentiment across key battleground states can still narrow margins significantly.

Ultimately, the November midterms will serve as a referendum on the current administration's policies and executive decisions. As campaigns enter their final weeks, both parties are pouring unprecedented financial resources into competitive districts and states. The resulting balance of power in Congress will profoundly shape American legislative priorities for the remainder of the presidential term.