There are 470 seats in the United States Congress up for election this year, but the direction of the next two years could come down to only a fraction of them.
A net increase of four seats in either chamber could bring change to the country, and the rest of the world.
"Almost every president in US history has had to navigate a divided Congress where the other party controls one or both houses," said Ava Kalinauskas, a senior research associate at the United States Studies Centre.
It's a reality Trump could face later this week, after a dramatic electoral cycle marked by costly campaigns and controversies — including a race featuring two candidates with almost identical names , another in which a failed Democratic candidate endorsed the Republican contender , and a Republican attack ad that drew bipartisan condemnation .
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Presidential elections are held every four years in the US. In the middle of a president's term, citizens vote for all members of the House of Representatives and a third of the Senate.
A hundred senators serve staggered six-year terms, while the 435 members of the House only serve for two years.
Kalinauskas says midterm elections are typically considered "a referendum on the current administration".
Voting will take place in the US on Tuesday 3 November, which runs from late Tuesday through to Wednesday afternoon in Australia.
Early results will start emerging after the polls close, which vary by state as elections are not federally regulated.
Most votes should be counted on election night, but in close jurisdictions, official results may take longer.
Cost of living is top of mind for many voters ahead of the midterms.
"We've seen polling that shows Americans feel financially worse off compared to when Trump was first in office, which is usually a telltale sign that they'll punish the incumbent," Kalinauskas said.
Other key issues include immigration, trade, corruption and the war on Iran, which has proven unpopular.
With recent surveys suggesting more than two-thirds of Americans think the country is headed in the wrong direction, she says these factors are "really motivating voters to the ballot box".
No, Trump is not on the ballot. His term continues until the next presidential election at the end of 2028.
The midterms will, however, shape what he can do over the remaining two years.
Kalinauskas says the president's party is "almost always punished" in the midterms.
"Throughout history, we see that the president's party loses an average of 27 seats and it's likely to be the same case this cycle," she said.
In Trump's first term, Republicans lost 41 seats in the House, but gained two in the Senate.
Ahead of the midterms, multiple state legislatures have redrawn electoral boundaries — a process known as gerrymandering .
"We have seen these tit-for-tat attempts from both parties to use gerrymandering as a way to cement gains for their party in the lead-up to the midterms," Kalinauskas said.
"The Republicans, in particular, really were able to tilt the map in their favour.
"But we're now seeing that some of those gains might actually not hold."
Unlike in Australia, the president does not need a majority in the House of Representatives to lead the country.
A president can lead a unified Congress, where their party controls both chambers, or a divided Congress, where their party has partial or no control over the chambers.
In his first term, Trump led a unified Congress before the Democrats flipped control of the House.
For the first half of his second term, he has governed with the support of a Republican-controlled Congress. Whether this remains for the next two years may come down to a slim margin.
The Democrats need only a net gain of four seats in the House and/or the Senate to take control of one or both chambers.
Kalinauskas says this would give the party the "opportunity to hamstring the Trump administration's agenda in different ways going forward".
While the president has some executive power, Congress is responsible for federal laws, the budget and holding the president to account.
Kalinauskas says Senate races tend to be more interesting and this year is no exception.
"There are definitely some curious dynamics that I'll be watching and some races that could make history," she said.
Several states traditionally considered Republican strongholds appear to be facing tight races this week, including Texas and Kansas.
Kansas holds the record for the longest continuous streak of single-party control of Senate seats. The last time the state elected a Democrat was in 1932. More than 90 years later, the Democratic candidate is polling narrowly ahead of the Republican incumbent before voters head to the polls.
In Michigan, Abdul El-Sayed is the Democratic candidate running against Republican Mike Rogers. On Tuesday, Haley Stevens, who lost the Democratic primary to El-Sayed, endorsed Rogers and appeared with him at a church service .
El-Sayed is backed by the Democratic Socialists of America. Kalinauskas says his performance will give some insight into "where Democrats go from here in terms of messaging, with an eye to 2028".
Other key battleground states include Alaska, Georgia, Iowa, Maine, North Carolina, New Hampshire and Ohio.
