As Americans go to the polls to vote for a new president, election battles for control of both chambers of Congress are also taking place around the country.
All 435 seats in the House of Representatives and 34 seats in the Senate are up for grabs.
Republicans currently hold a majority in the House, while Democrats control the Senate, both by slim margins.
Polls suggest the two parties could switch control of each chamber, with Democrats winning back the House and Republicans retaking the Senate.
The two parties are fighting over a handful of seats that could make the difference in how much power they hold in Washington in the new year.
Here is a guide to the crucial contests to keep an eye on.
Montana's Jon Tester faces his toughest test
With Republicans all but assured of flipping an open seat in West Virginia, Montana might cement the party's path back to a Senate majority - if they can oust three-term Democrat Jon Tester.
Tester, 68, is a third-generation dirt farmer re-elected twice on a pledge to be an independent voice willing to buck his own party. But critics argue he has been the deciding vote for much of President Joe Biden’s agenda and, as Montana has lurched rightward, his days in Washington could be numbered.
His opponent, Tim Sheehy, is an ex-Navy Seal who ran an aerial fire-fighting business that helps put out wildfires across the state. But the political novice has faced scrutiny over his background, including lying that the bullet in his arm is a wound from Afghanistan when he had in fact accidentally shot himself on a hike.
Sheehy, 38, has largely avoided the media but his embrace of Donald Trump may be enough to get him over the line.
Is Ted Cruz's time up in Texas?
Democratic efforts to oust Senator Ted Cruz six years ago fell short by some 200,000 votes. They now have another chance at defeating the Texan senator - with a new challenger.
Colin Allred, 41, is a former National Football League (NFL) player turned civil rights lawyer who served in the Barack Obama administration and is currently serving in the US House. He has attacked Cruz for vacationing in Mexico during a historic winter storm in 2021, and for voting to overturn Donald Trump’s 2020 election defeat.
Reproductive rights and Texas’s near-total abortion ban are also shaping the race, with Kamala Harris recently making a rare campaign trip to the state alongside Houston native Beyoncé.
Cruz, meanwhile, has vowed to “keep Texas, Texas” and extend Democrats’ three-decade lockout from state-wide office.
Wisconsin's Tammy Baldwin in tight race
Two months ago, Tammy Baldwin was coasting to re-election with a comfortable lead in the polls, money in the bank and Kamala Harris reinvigorating the Democratic ticket. But the first-ever openly gay US senator has seen her polling lead evaporate.
Republican Eric Hovde, 60, has dumped $20m (£15m) of his own wealth into the contest, endeared himself to Trump voters by leaning into the culture wars and blanketed the airwaves with negative ads tying Baldwin, 62, to inflation and illegal immigration.
If elected, the former banking executive and real estate mogul would be near the top of the Senate’s rich list and Democrats have cast him as making an opportunistic bid for office despite an inability to relate to working-class Wisconsinites.
But, in this crucial swing state, the flood of Republican cash is hurting both Baldwin and Harris - and twin defeats here could be a major blow for Democrats.
Will Ohio's Sherrod Brown defy the odds again?
As with Jon Tester in Montana, the ground has been shifting right throughout Senator Sherrod Brown’s three terms representing Ohio and he is currently the lone Democrat holding state-wide elected office.
But Brown, 71, has long been supported by Ohio union workers and blue-collar labourers, and he has stuck close to this voting bloc - which includes many Trump supporters - in his campaign for re-election.
Opposing him in what is now believed to be the most expensive Senate race in US history is Bernie Moreno, a Colombian immigrant and former auto sales magnate who portrays the veteran progressive lawmaker as “too liberal for Ohio”.
The 57-year-old inadvertently centred abortion access as a race-defining issue when he joked in September that “it’s a little crazy” for older women to care about the issue. Polls suggest it is hurting Moreno with suburban women.
The path to a House majority runs through New York
Half a dozen suburban swing districts in New York state likely hold the key to control of the US House next year.
Five of these districts are held by first-term Republicans, who carved out upset victories in the 2022 midterm elections on the back of voter concerns over crime, inflation and immigration.
But after facing criticism over party in-fighting and electoral infrastructure, Democratic leaders have invested millions into their New York operation this time around and are banking on high presidential election-year turnout.
Their candidates have, however, had to balance their messaging between offering solutions and acknowledging both the rising cost of living and high numbers of undocumented migrants that has cost taxpayers $2.4bn (£1.8bn) this year.
Democrats need to flip only four seats to win back a House majority. If they prevail, Hakeem Jeffries will become the first black House Speaker in history - and the first from New York since 1869.
Do the 'Blue Dog' House Democrats bite?
During the Joe Biden administration, no Democrats voted more out of step with their party leader than the so-called “Blue Dogs” - a cadre of 11 pro-worker populist House members.
From Jared Golden in Maine and Marie Gluesenkamp Perez in Washington state to Henry Cuellar in Texas and Mary Peltola in Alaska, this working-class caucus of lawmakers has regularly backed away from party priorities.
They have worked across the aisle to build bipartisan consensus, including helping craft a package earlier this year to provide funding for border security as well as aid to Ukraine and Israel. Senate Republicans tanked the bill after facing pressure from Donald Trump.
Democrats have been bleeding support in rural America for years, but successful re-election bids by the Blue Dogs could prove key for the party.
Nebraska's Don Bacon faces the fire
Four-term Nebraska congressman Don Bacon, 61, is part of a dying breed of moderate Republicans on Capitol Hill.
Donald Trump campaigned to replace Bacon two years ago.
But in May, he defeated a primary opponent who argued he was not adequately supportive of Trump. And though Bacon now has Trump’s endorsement, he supported Nikki Haley in the presidential primary race.
Bacon’s district also holds outsized importance in the presidential race. Unlike most other states, Nebraska splits its Electoral College votes by congressional district. Trump won the district in 2016, but lost it in 2020 and polls suggest he will lose it again this year.
Facing off against Bacon in a rematch of their 2022 contest is state Senator Tony Vargas, 40. New district lines and an influx of new voters since then, as well as millions of dollars in Democratic spending, all favour Vargas - and Kamala Harris.
A re-drawn district in Alabama becomes a race to watch
The fight to represent Alabama’s second congressional district is particularly interesting.
The district has been dominated by Republicans for the past six decades - but the US Supreme Court ordered it to be redrawn last year. In its ruling, the nation’s top court concluded that the southern state’s congressional map had likely been drawn in a discriminatory manner, concentrating black voters into just one of its seven districts.
The redrawn district is now majority black and it has set the stage for a highly competitive race between two lawyers and political newcomers - Democrat Shomari Figures and Republican Caroleene Dobson.
