Following the stunning election of Democrat Doug Jones in the Alabama Senate race, it’s even more likely to be a dramatic and vicious battle for control of the US Senate and House of Representatives next year.

Democrats now only need a net gain of two seats to win a majority in the 100-member upper chamber. Meanwhile, the party needs a net gain of 24 to retake control of the 435-member House.

Planned resignations and announced retirements are hitting Republicans harder. Of the 18 House members who have announced that they will not seek re-election in 2018, more than two thirds are Republican. Additionally, both House congressmen who will retire over the next few months are also part of the GOP. Special elections to fill those seats have not yet been announced.

As moderate Republican members get ready to depart Congress, conservatives want stronger allies in their seats, while Democrats see opportunities to turn them blue.

The campaign committees for both parties are looking at the 23 Republicans defending districts that Hillary Clinton won in 2016, and the 12 held by Democrats in districts that President Donald Trump won as vulnerable seats to flip.

In regard to the Senate races, several are expected to be very competitive. Mr Jones was able to pull off an upset in a deeply conservative state – strengthening Democratic momentum going into 2018 – but many party members still face tough re-election contests next year.

Several incumbents, such as Democratic senators Joe Manchin of West Virginia and Heidi Heitkamp of North Dakota, are running for re-election in states that overwhelmingly went to Mr Trump last year.

Texas Republican Senator Ted Cruz is also up for re-election. While many wouldn’t consider the Lone Star State a political battleground between Democrats and Republicans – the state has been a reliable Republican stronghold for the past few decades – a former Obama administration official sent a warning to Mr Cruz in the wake of Roy Moore’s defeat in Alabama.

“Be afraid, @tedcruz. Be very afraid” wrote former Secretary of Housing and Urban Development Julian Castro on Twitter. Mr Castro served as the mayor of San Antonio prior to joining the Obama administration.

Here are some possible big battlegrounds in 2018.

Alabama Senate race: Roy Moore vs Doug Jones Show all 12 1 /12 Alabama Senate race: Roy Moore vs Doug Jones Alabama Senate race: Roy Moore vs Doug Jones Democratic senatorial candidate Doug Jones speaks to reporters after voting Getty Images Alabama Senate race: Roy Moore vs Doug Jones Republican Senatorial candidate Roy Moore (L) and his wife Kayla ride their horses to the polling station to vote AFP/Getty Images Alabama Senate race: Roy Moore vs Doug Jones David Watson waves in a Santa suit as he holds a Doug Jones sign AP Alabama Senate race: Roy Moore vs Doug Jones Republican Senatorial candidate Roy Moore speaks to the media as his wife Kayla (R) looks on AFP/Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Alabama Senate candidate Doug Jones casts his vote at Brookwood Baptist Church REUTERS Alabama Senate race: Roy Moore vs Doug Jones Roy Moore speaks to the media after he rode in on a horse to vote AP Alabama Senate race: Roy Moore vs Doug Jones Democratic candidate Doug Jones greets supporters after casting his ballot AP Alabama Senate race: Roy Moore vs Doug Jones Republican Senate candidate Roy Moore departs on horseback after he cast his ballot in Gallant REUTERS Alabama Senate race: Roy Moore vs Doug Jones Voters wait in line to cast their ballot at a polling station setup in the St Thomas Episcopal Church Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Senatorial candidate Doug Jones (L) greets voters outside of a polling station at the Bessemer Civic Center Getty Images Alabama Senate race: Roy Moore vs Doug Jones Voters exit after casting their ballots at a polling station setup in the Fire Department Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Alabama U.S. Senate candidate Doug Jones speaks with the media after casting his vote at Brookwood Baptist Church Reuters

Arizona

Republican Senator Jeff Flake has announced he will not run for re-election in 2018, likely upending the race for his seat by doing so. It’s looking to be a tough primary fight for Republicans in the Republican-leaning state. The winner of the could face Democratic Representative Kyrsten Sinema, who is considered the Democratic Senate primary front-runner.



Florida

In 2016, President Donald Trump won 49 per cent of the vote in Florida while his Democratic opponent Hillary Clinton won 48 per cent. This fact alone could make Democratic Senator Bill Nelson’s re-election bid his toughest yet.

Indiana

The state handily went to Mr Trump in 2016 and is the home of Vice President Mike Pence. The Democratic incumbent, Senator Joe Donnelly, won his underdog race for the Senate in 2012 partially as a result of blunders by his Republican opponent. He may not get so lucky in 2018.

Missouri

Missouri is another state that strongly preferred Mr Trump over Ms Clinton last year, with 57 per cent of the vote going to the Republican candidate. Mr Trump has already targeted the re-election bid of Democratic Senator Claire McCaskill on Twitter, predicting a Republican candidate will take her seat in 2018 because she has opposed his proposed tax cuts.

Nevada

Republican Senator Dean Heller won his last election by just 1 point, and his state has become more Democratic since then. Nevada was also of the few battleground states Ms Clinton won in 2016, when Nevada voters also elected the US’s first Latina senator, Catherine Cortez Masto.

Minnesota