Here's What You Need To Know About The US Midterm Elections

The poll that could see Donald Trump's presidency seriously damaged -- but how do they work?

America's political system is similar to Australia's in many ways, but very different in others -- including the midterm elections which are set to be held on November 6.

For instance, Australia and the US both have two houses of parliament, both called the House of Representatives and the Senate.

But while Australia's Prime Minister is the leader of the party which has the most House seats, America has separate elections for president and for their Congress -- meaning the president can, and often does, represent one party while another party controls the parliament.

(Photo by Stefan Zaklin/Getty Images)

Donald Trump's Republican party currently controls both houses of US Congress, but Tuesday's election could see the Democrats wrestle back at least one chamber, which would make Trump's life hell.

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So what are the midterm elections?

America holds elections every two years. A presidential term runs for four years, so the biennial elections -- coming halfway through the president's time in office -- are called 'midterms'.

At these elections, all 435 seats in the House are up for grabs, while one-third of the Senate is also running. Senators' terms run for six years, meaning they only stand for election every three polls, with 33 senators going to the polls each time.

A joint session of Congress  (Photo by Chip Somodevilla/Getty Images)

Midterms, coming two years after the president is elected, are often seen as a barometer on the president's performance.

How do the midterm elections work?

All 435 congressional districts around the country go to the polls to vote for their local representative. There's another 33 senators also up for re-election, while another two Senate vacancies will be filled after resignations, and nearly 40  on the ballot cards in various states, while nearly 40 state governors will be chosen as well.

That's more than 500 elections happening on the same day all across the country, a mammoth effort that could see the entire balance of power shift in US politics.

What's at stake in these midterm elections?

To be blunt, it could end Donald Trump -- but it almost certainly won't. It will likely seriously damage his presidency though, and make it harder for him to make the changes he wants.

The Democrats need to win 23 seats to gain the balance of power in the House. Considering the president's party has lost an average of 30 seats at every midterm in the last four decades, and considering Trump's own personal political disasters, there is a better than good chance the Democrats could win back the House.

Donald Trump addresses a joint session of the US Congress (Photo by Jim Lo Scalzo - Pool/Getty Images)

But winning the Senate will be hard. The Republicans only have a one-seat majority in the upper chamber, but a kink of history means far more Democrat senators are up for re-election, meaning the blue party could even lose some seats there and have fewer chances to wrestle Republican Senate spots.

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But even if the Democrats only win back one house, they can make Trump's life hell. They could move to further investigate his business dealings and ties to Russia, or even impeach the president.

That last option seems unlikely, but it could happen.

Are the Democrats likely to win back the House?

Based on history, yes. Presidents almost always lose seats at their first midterm election, after their opponents ramp up efforts to get voters to the polls and capitalise on unpopular decisions to fire up their supporter base.

The Democrats have been running huge campaigns against Trump's divisive rhetoric and policies, signing up scores of new and young voters, and inspiring their supporters to get out and vote.

(Photo by Chip Somodevilla/Getty Images)

While Trump isn't on the ballot, polls show voters are upset with his work, and many Republican politicians who are closely aligned with Trump are looking likely to lose their seats.

How are US elections different to Australia's?

Similar to Australia, representatives stand for their local area, and seats are split so that each congressman represents roughly 700,000 people -- but unlike Australia, where electorate borders are often drawn quite simply, American districts often undergo controversial alterations called 'gerrymandering'.

This involves district borders being redrawn, often in bizarre and convoluted shapes, to benefit the party in power -- such as the Maryland 3rd or several in Ohio, as can be seen in the below pictures. For instance, borders can be redrawn so that large pockets of people who vote for the Democrats can be removed from a Republican district, or vice versa.

Maryland 3rd (in orange)
Ohio districts

Another key difference is that Americans aren't compelled to vote. Unlike Australia, where our compulsory voting system means we are usually fined if we don't vote, American voters don't have to head to the polls if they don't want to. It also means you hear a lot about terms like 'voter suppression', where people make it harder for voters to cast a vote.

That might be by putting polling places in difficult-to-reach locations, making it difficult to travel to or enter polling places, or bosses not giving their employees time off work to lodge their ballots.

One example is in Dodge City, Kansas, where controversy has erupted after the only polling booth was placed out of town, making it difficult for voters to reach.

How can I follow along?

Americans vote on Tuesday (US time) so we'll start hearing results on Wednesday morning (AEST).

Stay tuned to 10 daily from Wednesday morning as we bring you all the results and washup, including coverage from 10 News First senior reporter Hugh Riminton on the ground in Washington DC.