If Democrats capture the House, they could block Mr Trump's agenda and launch congressional investigations into aspects of Mr Trump's administration, from his tax returns to possible business conflicts of interest and the nature of his 2016 campaign's ties to Russian Federation.
Republicans are expected to retain their slight majority in the US Senate, now at two seats, which would let them retain the power to approve US Supreme Court and other judicial nominations on straight party-line votes.
Republicans have retained Senate control for two more years.
What happens on election day?
He and the first lady were to host an evening watch party for family and friends.
"There was a woman in front of me who had two children, and she had to have her kids save her spot in line so she could go back to her auto for a second".
Sanders added that the president provided voters with a choice between "American prosperity and security" and going "backwards".
On Tuesday night, he called to congratulate Pelosi and acknowledged her plea for bipartisanship, the leader's spokesman said.
Polls in Virginia and Florida begin closing at 7 p.m. ET with the majority closed by 9 p.m.
Polls in some 20 states - including MA - will close at 8 p.m., just after Ohio, West Virginia, and North Carolina wrap things up at 7:30 p.m. With the first polls not slated to close until 6 P.M. eastern, polling was the only indicators both parties had on Tuesday of their prospects.
Vermont independent Sen. Bernie Sanders and Democrats Elizabeth Warren of Massachusetts, Kirsten Gillibrand of NY and Minnesota's Amy Klobuchar were easily re-elected. And Massachusetts Sen. Elizabeth Warren, another potential 2020 contender, also won her race.
Jay Ghazal, a political consultant and former Congressional aide says the Democratic majority in the House will also have some effects on Trump's foreign policy: "The House will be able to vote to increase foreign aid, something the president has been cutting".
A surge in early voting, fuelled by a focus on Trump's nationalistic, norms-breaking presidency by supporters of both parties, could signal the highest turnout in 50 years for a midterm U.S. election when the White House is not on the line.
"We did have two maniacs stop a momentum that was incredible, because for seven days nobody talked about the elections", the President said at a Missouri rally last week.
"We have already seen a huge turnout, people out and about knocking on doors, making sure everybody gets out there, but I think turnout will be very, very high", Democratic candidate Katie Porter, who is running in Irvine, California, against two-term Republican incumbent Mimi Walters, told AFP.
Quorum rules say 20 senators must be on the Senate floor and 40 representatives on the House floor for votes to take place, Courtney said.
As to the Senate, Republicans have a much better chance of keeping control.
Alongside all 435 House seats and a third of the Senate on the ballot on Tuesday are 36 gubernatorial races. More women than ever were running, along with veterans and minorities, many of them motivated by revulsion over Trump. The results will start coming in shortly after the voting concludes.
Hannah Ackermann said officials at the polling site offered various explanations for the delay, including blaming workers who didn't show up and overloaded machines.
A loss of the House will also trigger significant second guessing of the President's tactics, given that he chose not to make the booming economy his primary midterm argument, instead turning to a searing indictment of Democrats focusing on immigration and laden with racial language.
Health care has been the dominant message for Democrats this cycle - mentioned in more than half the party's TV ads.
Ilhan Omar, a Somali refugee, won a House seat in a heavily-Democratic district in the Midwestern state of Minnesota, where she will succeed Keith Ellison, himself the first Muslim elected to Congress.
Unlike 2016, however, Democrats have historical trends on their side.
Democrats were riding to victory Tuesday with strong support from women turned off by Trump's bullying style and among suburban voters with higher incomes and education levels.
"Most of the candidates that the president actually went in and campaigned for and who embrace the president are doing well tonight", she said.
Stephen Myrow, managing partner at Beacon Policy Advisors, discusses how the markets are poised to react to the USA midterm election results.
In recent years, as America has grown more deeply divided along partisan lines, this is becoming the case less and less.
Lavrov said he is hopeful that the election will help stabilize domestic politics in the U.S.
Election workers Mark Bezanson, left, and Julie Olson dump ballots collected earlier in the day from drop boxes onto a table for sorting at the King County Elections office, Monday, November 5, 2018, in Renton, Washington.