A divided government is a real possibility in the United States, and the House of Representatives is the most likely chamber to swing from Republican to Democratic control in Tuesday's midterm elections.

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The must-watch Senate races

The must-watch Governor races

The Democrats need a gain of 23 seats to take control of the 435-seat House, and the Republicans are firmly on the defensive. FiveThirtyEight puts the chances of Democrats seizing control of the chamber at seven-in-eight.

The Cook Political Report shows that a whopping 79 seats are toss-ups or marginally favor one party and, with 73 of them currently in Republican hands, that's good news for the Democrats.

A Democrat-controlled House could be a nightmare for President Donald Trump, with the party setting the legislative agenda as well as holding the power to call hearings and demand investigations. 

That would put Trump's domestic agenda on the floor and probably lead to a greater focus on foreign policy, as well as lead to probes into his administration and personal affairs – potentially even leading to impeachment.  

Here are eight high profile battles likely to make headlines on election night:

- Republican Steve King, the incumbent congressman in Iowa's fourth district, has seen his polling lead shrink after attracting national attention with racist comments.

- Democrat J.D. Scholten trails by an average of seven points, but has closed the gap rapidly in recent weeks and is in with a shot. 

Why it matters:

The race has hit headlines because of the antics of Republican King, whose racist rhetoric has shocked members of his own party as well as Democrats. The election is a test of just how much Iowan voters are prepared to take. 

- Republican Pete Stauber looks set to take the open Minnesota eighth seat according to the latest New York Times/Siena poll, which gives him a huge 15-point lead. 

- Democrat Joe Radinovich will miss out in a district that voted for Obama in 2012 if the latest data is to be believed, but a shred of hope lies in a September poll that gave the Democrat a one point advantage. 

Why it matters:

Retired police officer Stauber symbolizes the changing Republican Party: He is both pro-union and pro-Trump. He has a huge chance to flip the Democratic Minnesota's eighth district which Trump won by 16 points in 2016, and both the president and vice president have dropped in for campaign stops.

- Republican Kevin Yoder could be set for a big defeat in Kansas' third district, with the incumbent down double digits in the latest poll from Emerson.

- Democrat Sharice Davids, a former lawyer and martial arts fighter, is in a strong position to flip the district as her party looks to make gains in red states. 

Why it matters: 

Davids would be the first Native American woman in Congress if she were to win. A Democrat has only held the district in deep red Kansas once since 1961 and Trump won the state by a massive 21 points in 2016, but the third district itself went narrowly to Clinton. The National Republican Congressional Committee has cancelled a one million US dollar ad buy for Yoder -- not a sign of confidence. 

- Republican Brian Fitzpatrick holds a 2.5-point polling average lead in Pennsylvania's first district.

- Democrat Scott Wallace trails in the polls but Clinton won the district narrowly in 2016, suggesting he's still in with a shot of flipping it blue.

Why it matters:

Where many Republican candidates have leant on the power of Trump, incumbent congressman Fitzpatrick is a centrist who has kept a distance from the president. Wallace is a wealthy establishment Democrat who has funded his own campaign. The race hails back to the pre-Trump era.

- Republican Mark Harris is hoping his Trumpian approach will keep North Carolina's ninth district in his party's hands, but the firebrand pastor is neck-and-neck in recent polls.

- Democrat Dan McCready is hoping his military service will help him attract moderate Republican voters and take a surprise win. 

Why it matters:

A Democrat hasn't been elected to North Carolina's 9th district for more than half a century and Trump won it in 2016 by 11.6 points, but Iraq war veteran and Harvard Business School graduate McCready is in with a shout after Republican primary voters opted to kick out incumbent Robert Pittinger. Harris, a pastor, has taken extreme positions likely to alienate moderate Republicans. 

- Republican Jeff Denham is the incumbent in the 10th district, but going into election day polls put him two points behind in a state where big swings are expected.  

- Democrat Josh Harder has a good shot of flipping the district as Democrats look to make big gains across California. 

Why it matters:

If the Democrats do win back the House, California will be a key state. The party is targeting a number of Republican-held districts that were won by Hillary Clinton in 2016. The battle in the 10th district is particularly high profile: Incumbent Jeff Denham is fighting to keep his seat against a strong challenge from Harder. 

- Republican Dave Brat is the right-wing incumbent in Virginia's seventh district but polls suggest he's level-pegging this time around.

- Democrat Abigail Spanberger is a former CIA officer who is hoping her law enforcement past will attract moderate Republicans. 

Why it matters:

Republican Brat took a big Democratic scalp when he beat House Majority Leader Eric Cantor in 2014, but the member of the ultra conservative House Freedom Caucus is struggling this time around. The latest polls put him two up, one down and all-square against Spanberger in the traditional bellweather district. The Democrats hope her law enforcement past will help persuade moderate Republicans lend her their vote and flip the district blue. 

- Republican John Faso is the incumbent congressman in a district Trump won by almost seven points in 2016, but recent polls suggest the race is too close-to-call.

- Democrat Antonio Delgado, a Rhodes Scholar and former rapper, is pushing his veteran opponent all the way in what has been a controversy-laden race in New York's 19th district. 

Why it matters:

The fight in the district north of New York City has been particularly dirty. Delgado, standing in his first election, is a Rhodes Scholar and Harvard Law School graduate. He also released a rap album in 2006, and the Republicans have used images of him performing in what Delgado claims is a racial attack in a 90 percent white district. The contest is a microcosm of the national campaign argument: Healthcare versus cultural issues. 

(Graphics by Zhao Hong and Yin Yating)