ByMike Hills
Visual Journalism team
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.
Midterms come at bad time for Trump
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 battle for the House
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, 15 are currently held by Republicans and six by Democrats. If the Democrats win five of those on top of 28 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, external going back to 1934. Of those 23 elections, the president's party has only made gains in three.
The battle for the Senate
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 six-year terms so roughly a third are up for election every two years.
Thirty-five seats are up for grabs in November but analysis by the Cook Political Report suggests that only seven of them are toss-ups that could go either way.
Of those toss-ups, six are currently held by Republicans and one by Democrats. The Democrats would need to win four of those seats, plus the four classed as likely or leaning Democratic, to hit 51 and take control of the Senate.
But winning a majority is no easy task for the Democrats.
They need to keep hold of their seat in Michigan, where polls suggest the race is tighter than Democrats would like between Abdul El-Sayed, a left-wing political outsider, and his Republican rival Mike Rogers, a Trump ally and former FBI agent.
And they would also need to pick up seats in states that Trump won by double-digits in 2024, including Alaska, Iowa and Ohio.
But polls suggest they have a chance, even in Texas where former teacher James Talarico could become the first Democrat to win a Senate seat in the state since 1988 if he defeats Ken Paxton, the current state attorney general and close Trump ally.
What are the key issues for voters?
Trump pledged to "end inflation and make America affordable again" in his 2024 election campaign but the cost of living crisis is proving to be the key issue for voters.
The president proudly declared that gas was "now below $2.30 [£1.74] a gallon in most states" in his State of the Union address on 24 February. But the war with Iran began four days later, disrupting Middle Eastern energy supplies and causing gas to hit $4 (£3.03) in the US.
The war became increasingly unpopular as its consequences reverberated around the world and ultimately hit American consumers in the pocket. One poll carried out in August found 63% of respondents disapproved of Trump's handling of the situation.
Other issues that voters say are important to them include healthcare and immigration.
Trump has recently touted his policies around immigration as a big success, citing significantly lower border-crossing figures than in recent years.
Many Democratic candidates are focusing on the high costs of US health insurance and the impact of Trump's legislation on access to the healthcare system.
Can Trump defy political gravity?
Most signs point towards a successful midterms for the Democrats, but it wouldn't be the first time that Trump and his party have outperformed polls if they do win more seats than expected.
One of the few things in their favour is their huge financial advantage.
At the end of August, the Republican National Committee and its allied groups had more than $600m (£455m) cash on hand, while the Democrats had just under $400m (£303m).
On top of that, the Republicans also had more than $400m held by Trump's MAGA Inc group, the main fundraising and spending arm of the "Make America Great Again" political movement.
The Republicans are using that financial advantage to buy advertising.
More than $1bn worth of political ads were broadcast to US voters in September, according to research firm AdImpact, external. Republicans spent $200m more than the Democrats and outspent them in nearly all of the Senate races classed as toss-ups.
Trump will be hoping this late messaging blitz can help convince Republicans to get out and vote in November, boosting turnout and limiting the damage done to him and his party.
Whatever the result, attention will quickly turn to the next presidential election in 2028. Trump's unpopularity has dominated the midterms, but with him constitutionally unable to run for a third term the focus will shift to what the Democrats stand for, not just what they stand against.