Voters in the United States are heading to the polls to cast their ballots in the "most important midterm election" in the country's history.
That's according to US President Donald Trump, whose record over the past two years appears unlikely to be judged favourably.
Midterm elections — where voters choose their congressional representatives, some senators, and most governors — are often viewed as a referendum on the incumbent administration's performance.
Polling suggests Democrats will do well, but whether the results will meaningfully affect the remaining two years of Trump's presidency remains to be seen.
"[Republicans] will expect to lose the House of Representatives," associate professor David Smith of the United States Studies Centre at the University of Sydney told SBS News.
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"If they lose the Senate, that is a sign that they've had a really bad election."
A Democratic takeover of either chamber would make it much harder for Trump to advance his legislative agenda during the remainder of his term, and would likely subject his administration to greater scrutiny, including Democrat-led investigations.
US politics professor Brendon O'Connor, also of the US Studies Centre, told SBS News that, no matter the results, Trump is unlikely to accept them gracefully.
"That would lead to more of this tension and conflict and extreme partisanship that we've seen," he said.
"It is consequential for the Albanese government in the sense that you might even have a more erratic Donald Trump to deal with."
Heading into the 3 November election, Trump has a net approval rating of -20.4, the lowest of any US leader at this stage of their term since post-war leader Harry S Truman.
Currently, Republicans control both the US House of Representatives and the Senate, with the latter a more difficult hurdle for the Democrats.
All 435 seats in the House will be voted on across all 50 states, and Republicans are defending a slim majority of 218 to the Democrats' 214, with one seat held by an independent and two vacant.
The Washington Post is forecasting the Democrats will win 235 seats.
Leading US statistician and electoral analyst Nate Silver's latest forecasting and polling aggregation shows the Democrats have a 96 per cent chance to win the House.
Kalshi, the US online betting market , gives Democrats a 93.3 per cent chance of House control.
The Senate is held 53-47 by the Republicans, and only a third of seats will be contested on Wednesday. However, more of those are Republican-controlled, giving the conservative party an advantage.
Still, Silver's analysis holds there is an 82 per cent chance the Democrats will claim the Senate, while Kalshi suggests a 75 per cent chance.
The Post forecasts Democrats will walk away with a 52-48 seat majority.
While all House seats and 35 Senate seats are in contention, the impact of gerrymandering and political polarisation in the US has resulted in a dwindling number of those being true contests.
For the House, roughly 30 to 45 seats are expected to be genuine swing districts. These are mainly in the commuter suburbs of New York and California, as well as in the Rust Belt states of Philadelphia, Michigan, and Ohio.
Sun Belt voters in Arizona and Nevada could also play a key role, as could agricultural workers in Iowa, Nebraska, and Washington.
The Senate battlegrounds look different. With two senators in each state, Democrats need to flip four Republican-held seats to take control.
Roughly 10 Senate races are expected to be in true contention: Alaska, Iowa, Kansas, Maine, Michigan, Ohio, Texas, New Hampshire, North Carolina, and Georgia.
Significant focus has been given to the battle between Democrat James Talarico and Republican Ken Paxton in traditionally red Texas, as well as to the contest between the potential first Muslim senator, Democrat Abdul El-Sayed, and Republican Mike Rogers.
"If the Republicans lose Texas, that's going to send a shockwave through the party," O'Connor said. "Because they really can't win the presidency [in 2028] if they lose California, New York, and Texas. That's a real disaster."
Democrats have, however, been accused of planting an independent candidate in Alaska with the same name as the Republican incumbent , playing into the hands of Trump's often-cited election tampering claims. Democrats have denied any involvement in his candidacy.
"If the Democrats hold a 51-seat majority because of Alaska, that is going to be a big story and a total mess," O'Connor said. "And the Democrats will be seriously blamed for that."
Trump has made little effort to assuage voter concerns about the rapidly rising cost of living in the US. During a final campaign rally in Georgia, he bragged to the crowd that US oil companies were making "a freaking fortune" due to the war he launched in Iran.
It's messaging that has not gone down well, Smith said, with frustrated voters who turned to Trump in 2024 and are now even more frustrated at his failure to address their main issue.
"Trump has record low approval ratings, and people's feelings about the economy are very bad," Smith said. "The fact that people can't keep up with the cost of living has been the central source of frustration for Americans for the last five years.
"That was a problem Trump promised to fix, but instead, people can see that he has made it worse."
With "nothing cutting through" on the economy, Republican campaigning has largely focused on culture war issues, with Trump telling Fox News the number one reason to vote Republican on Wednesday is because of the rising threat of "communism".
Islamophobic attacks on Senate hopeful El-Sayed and anti-transgender rhetoric have also been a key feature.
"They're just trying to depict Democrats as too weird and too extreme for the country," Smith said. "That may have worked better in 2024. It doesn't seem to be working so well now."
Perhaps tellingly, New York Times analysis found that just 1 per cent of Republican campaign ads mention Trump. By comparison, 20 per cent of Democratic ads mention him.
Trump, who used his final address before the ballot to champion his Washington renovations, has promised every US citizen US$5,000 ($7,165) if the Republicans win, a policy that would cost an estimated US$1.2 trillion ($1.71 trillion).
While polling "looks good" for the Democrats, O'Connor cautioned that the results would have to be truly exceptional for them to gain some of the deep red territories they have been tipped to win.
"The Democrats haven't won Kansas since 1932 when Roosevelt came in on a landslide," he said.
"South Carolina, Kansas — it would be a remarkable repudiation if Trump loses in those kinds of places.
"I'm going to be waiting. I'm not putting any money on them."
US voters will go to the polls overnight, with the first results expected in the morning on Wednesday AEDT.
This election is expected to be the most expensive in US history, with campaign spending eclipsing the 2024 presidential election to reach US$11.6 billion ($16.6 billion).
