The long prophesied “blue wave” was not the tsunami the Democrats had hoped for, but the party did successfully wrest control of the House of Representatives, bringing an end to the triple-headed Republican power-hold in Washington DC.

The Democrats gained over 30 seats in the House to give them their first majority since 2006, during George W Bush’s second term, and which was lost in 2010 two years after Barack Obama took office.

The win installs a wave of diverse, progressive, first-time candidates in Congress, and the party immediately plans to take advantage of their newfound powers, which include being able to subpoena Donald Trump, relaunch probes into his 2016 presidential campaign and launch fresh investigations into his administration.

Democrat preparations for action in case of winning the House have reportedly been underway for months.

But the Republicans clung on to the Senate – the upper house – in an election that saw them defending nine seats – far fewer than the Democrats’ 26 which were up for grabs.

The Democrats may be in a stronger position than they have been in Congress for eight years, but without majorities in both congressional houses they will still struggle to block many of the Trump administration’s political moves.

US midterm results: more diverse, more female and more progressive Show all 20 1 /20 US midterm results: more diverse, more female and more progressive US midterm results: more diverse, more female and more progressive Democratic candidate Ilhan Omar is celebrates with her husband's mother after she won a congress place, becoming the first Muslim woman to be elected into congress alongside Rashida Tlaib Reuters US midterm results: more diverse, more female and more progressive Democratic House candidate, from Kansas, Sharice Davids (left) and her mom Crystal celebrate after she won. Davids is the first lesbian Native American Congresswoman by beating Republican incumbent Kevin Yoder. Davids is one of several first-time female candidates that helped the Democratic Party takeover in the House of Representatives EPA US midterm results: more diverse, more female and more progressive Republican Marsha Blackburn celebrates after winning the race for senate in Tennessee. In doing so she became that state’s first female senator AP US midterm results: more diverse, more female and more progressive Supporters of Democratic House candidate Sharice Davids cheer and cry after learning she won EPA US midterm results: more diverse, more female and more progressive Ayanna Pressley beaome Massachusetts’ first black congresswoman by defeating 10-term Republican Michael Capuano AFP/Getty US midterm results: more diverse, more female and more progressive Republican candidate Young Kim has become the first Korean-American woman elected to Congress AP US midterm results: more diverse, more female and more progressive Democrat Jared Polis won his seat and became the US’s first ever openly gay governor AAron Ontiveroz/The Denver Post via AP US midterm results: more diverse, more female and more progressive Jean Kasselman (left) and Teresa Booker, supporters of Democratic candidate for Kansas' 3rd Congressional District Sharice Davids, react to election results Getty US midterm results: more diverse, more female and more progressive Republican Kristi Noem hugs a supporter after being announced as the new governor of South Dakota. Noem made history by being the first female governor of the state AP US midterm results: more diverse, more female and more progressive Gabierla Martinez and Cesar Delgado cheer on Democratic gubernatorial candidate Jared Polis REUTERS US midterm results: more diverse, more female and more progressive Alexandria Ocasio-Cortez became the youngest women ever elected to Congress, representing New York’s 14th congressional district AFP/Getty US midterm results: more diverse, more female and more progressive Democratic congressional candidate Rashida Tlaib celebrates with family and friends at her midterm election night party in Detroit after won and also became the nation’s first Muslim woman to congress alongside Ilhan Omar who was also elected Reuters US midterm results: more diverse, more female and more progressive Supporters of Democratic candidate for Kansas' 3rd Congressional District Sharice Davids react to election results Getty US midterm results: more diverse, more female and more progressive Already having become the first Native American woman to chair a state political party, Deb Haaland has now become the joint-first Native American woman to be elected to congress, alongside Sharice Davids Reuters US midterm results: more diverse, more female and more progressive Supporters of Alexandria Ocasio-Cortez cheer during her election night party in the Queens Borough AFP/Getty US midterm results: more diverse, more female and more progressive Young Kim hugs her son Alvin after she won a seat in congress AP US midterm results: more diverse, more female and more progressive Supporters of Alexandria Ocasio-Cortez cheer AFP/Getty Images US midterm results: more diverse, more female and more progressive Asma Mohammed and Ashley Fairbanks celebrate as results come in at Democratic congressional candidate Ilhan Omar's election night headquarters AP US midterm results: more diverse, more female and more progressive Democrat Deb Haaland hugs a voter REUTERS US midterm results: more diverse, more female and more progressive Supporters of Democratic House candidate from Kansas Sharice Davids cheer and cry after learning she won her race EPA

With the Senate still on his side, Mr Trump will retain his ability to appoint his picks to the Supreme Court and Cabinet.

Nonetheless, the shift means Donald Trump could be forced to use diplomacy if he wishes to push through major pieces of legislation. Having spent his political career aggressively disparaging the opposition, the power shift could force the president to reassess his methods.

What can the Democrats do now they control the House?

Impeachment

With a Democrat majority there is likely to be a surge in investigations into the president’s numerous scandals and controversies – the party will have more money, staff, and control over the chamber’s committees. It is possible they could pursue formal impeachment action against Mr Trump, but there are major caveats and obstacles.

The House of Representatives can instigate impeachment proceedings, but it requires a majority House vote. With a Democrat majority, that is now much more likely, though many Democrats would be cautious about taking such action as historically such a move has generated a voter backlash.

Even if the House did take impeachment action, two-thirds of the Senate would then have to vote in favour of it, and the Republicans have strengthened their control of the Senate, making impeachment unlikely to be successful.

It is also thought Democrats are unlikely to make any serious moves towards impeachment until Robert Mueller’s investigation into election interference and possible collusion between Russia and the Trump campaign is complete.

Tax returns

Ever since Mr Trump announced his intention to run for president, his decision not to release his tax returns has been a major bone of contention.

Pursuing the elusive documents is said to be a top priority for the Democrats following their electoral success.

Representative Richard Neal, who is expected to lead the House Ways and Means Committee, told CNN in October he plans to first ask Mr Trump for them. Mr Trump has been asked to hand them over in the past, and has refused, but Mr Neal has said if the president does not hand them over, he will use an arcane IRS code to formally request them, a move expected to launch a lengthy legal battle.

But the documents could then be examined to see if Mr Trump had any business ties with Russia that could have led to Russian interference.

Russia

Speaking of Russia, a Democratic House could reopen the congressional investigation into Mr Trump’s relationship with Russia, which the Republican-led house closed in March. A reopened investigation would be informed by Mr Mueller’s ongoing probe, and would likely seek to go after any unanswered questions from that investigation in order to reveal more and put further pressure on the president.

Mexico border wall

In order for spending bills to be enacted, they need to be passed by both the House and the Senate. With a Democratic-controlled House, any Republican efforts to secure funding for a US-Mexican border wall could be blocked from passing.

The Republicans have said they are “committed” to ensuring they secure the funding for the president’s signature election pledge, but Democrats have signalled they are willing to fight border funding.

In August Mr Trump said he was looking for about $5bn (£3.8bn) in funding “for this coming year”, adding: “We’re building the wall, step by step.”

In March, Congress allocated $1.6bn (£1.2bn) in border spending – a portion of which will go towards replacing sections of existing border walls.

Healthcare

The two key issues on voters’ minds for the 2018 midterms appeared to be immigration and healthcare, with the Democrats running a strong campaign on protecting elements of improved affordability of healthcare insurance installed by the Obama administration.

The Democrats’ House leader Nancy Pelosi said after the midterms the party would focus on fighting to protect Medicare and Medicaid – long running programmes to provide health insurance to over-65s and disabled people regardless of income.

Democrats have also said they want to lower drug prices and health cover premiums and aim to protect Americans with pre-existing conditions from higher insurance premiums.

Dismantling Mr Obama’s health reforms have been a key aspect of Mr Trump’s legislative programme, but he struggled even to convince his own party that removing Obamacare in its entirety was a good idea.

US midterm elections: voters head to the polls Show all 28 1 /28 US midterm elections: voters head to the polls US midterm elections: voters head to the polls Beto O'Rourke talks with a supporters after he cast his ballot at El Paso Community College-Rio Grande Campus Getty Images US midterm elections: voters head to the polls Sarah Salem, 34, swims as voters cast their ballots at Echo Deep Pool in Los Angeles AP US midterm elections: voters head to the polls Abigail Spanberger, Democratic candidate to represent Virginia's seventh Congressional district in the US House of Representatives; casts her ballot to vote in the 2018 midterm general election, with her daughters Claire (L), Charlotte (Bottom C) and Catherine (R); inside a polling station located at Deep Run High School in Glen Allen, EPA US midterm elections: voters head to the polls A voter waits behind a line to cast their vote at a Fulton County polling place in Atlanta, Georgia REUTERS US midterm elections: voters head to the polls Representative Peter King and his wife Rosemary hand in their completed ballots as voters turn out at the Manor Elementary School in Seaford AP US midterm elections: voters head to the polls Two year old Mave Adilatta looks out from a voting booth as her mother casts her ballot in Cambridge, Massachusetts EPA US midterm elections: voters head to the polls Beto O'Rourke, candidate for US Senate, speaks with reporters after voting REUTERS US midterm elections: voters head to the polls A voters fills out their ballot for the midterm election at a polling place in Madison, Wisconsin REUTERS US midterm elections: voters head to the polls Congresswomen Elect Ayanna Pressley speaks to reporters after voting at the Adams Street Library AFP/Getty Images US midterm elections: voters head to the polls A sign showing voters where to cast their ballots in the 2018 midterm election in the Mt Airy neighborhood in Philadelphia EPA US midterm elections: voters head to the polls Democratic candidate for Vermont Governor Christine Hallquist leaves after voting in Hyde Park, Vermont EPA US midterm elections: voters head to the polls Members of the group Your Vote Matters place signs on an overpass in Saint Louis, Missouri EPA US midterm elections: voters head to the polls Voters cast their ballots at a polling station setup in a City of Hialeah Fire Station Getty Images US midterm elections: voters head to the polls Voters enter a polling station in Des Moines, Iowa Getty Images US midterm elections: voters head to the polls Volunteers with the Democratic party take cover from the rain as they wait to speak to voters outside of a polling station AFP/Getty Images US midterm elections: voters head to the polls Voters cast their ballots in the 2018 midterm election at the Fraternal Order of Eagles in Streetsboro, Ohio EPA US midterm elections: voters head to the polls Democratic candidate for Vermont Governor Christine Hallquist campaigns in Stowe EPA US midterm elections: voters head to the polls A voter of the Jewish community is seen leaving after he cast his ballot in the midterm election at the East Midwood Jewish Center polling station in the Brooklyn borough of New York City AFP/Getty Images US midterm elections: voters head to the polls A man wearing a New York Yankees hat votes during in Manhattan Reuters US midterm elections: voters head to the polls Voters line up to cast their ballot just before the polls open in the mid-term election in Miami Getty US midterm elections: voters head to the polls Voters cast their ballots at the Tuttle Park Recreation Center polling location in Columbus, Ohio AP US midterm elections: voters head to the polls Stickers that read 'I Voted' are seen at a polling station located at Deep Run High School in Glen Allen, Virginia EPA US midterm elections: voters head to the polls Poll workers check over voting machinery before voters arrive at Franklin School in Ohio USA EPA US midterm elections: voters head to the polls Voters cast their ballots at Immaculate Conception Parish Hall in Ravenna, Ohio EPA US midterm elections: voters head to the polls Election judges take the oath before opening a polling location in Arlington Heights, Illinois EPA US midterm elections: voters head to the polls Voters arrive at the Tuttle Park Recreation Center in Columbus, Ohio AP US midterm elections: voters head to the polls People vote in Manhattan Reuters US midterm elections: voters head to the polls A voter uses an electronic voting machine AP

Iran

Democrats were enraged by Mr Trump’s withdrawal from the international nuclear deal with Iran brokered by the Obama administration in 2015. But even with a House majority there is little they can do to change the policy as long as Republicans occupy the White House.

US politicians are also wary of seeming too friendly to Iran, especially given hostility to Tehran by the government of Israel. While Israeli Prime Minister Benjamin Netanyahu has worked increasingly closely with US Republicans, strong ties to Israel remain a top priority for both parties.

Trump’s future ambitions

Donald Trump has already registered his 2020 campaign slogan as “Keep America Great”. Is the Democrat House win a setback to his presidential ambitions?

Losing control of the House, is entirely in keeping with recent US political history and is unlikely to spell disaster for Mr Trump in the coming years.

Most presidents who lose one or even both houses in their first midterms go on to re-election – including Barack Obama, Bill Clinton and Richard Nixon.

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