"It's a huge moment and victory for the president", Press Secretary Sarah Huckabee Sanders told reporters at the White House Tuesday night.
With a House majority, Democrats will have the power to investigate Trump's tax returns and possible conflicts of interest, and challenge his overtures to Saudi Arabia, Russia and North Korea. She cited Mike Braun, who unseated Senate Democratic incumbent Joe Donnelly in IN and helped cement a Republican majority in the upper chamber, and who benefited from three Trump rallies on his behalf.
Trump was watching the results alongside friends and family at the White House, his spokeswoman said.
"Lavrov also reiterated Moscow's position that it is not meddling in USA elections".
House Minority Leader Nancy Pelosi was upbeat about the Democrats' chance of winning the House.
Pelosi says that after 2016 Democrats "didn't agonize, we organized".
"Trump is the dividing force in this election", noted the USA Today newspaper. Senate Majority Leader Mitch McConnell is widely expected to remain atop the conference, with Sen. "That's why we will be campaigning for every last vote in every part of our great country", he said.
Historically, the party of the president loses seats in Congress after a presidential election, a dressing-down of the chief executive from voters.
And by 9:30 eastern time, NBC had reported that Democrats would win enough seats to take back control of the House of Representatives.
In Indiana, Republican Mike Braun beat Democratic incumbent Senator Joe Donnelly.
Some of the biggest Democratic stars of the campaign lost.
In Florida, left-wing progressive Andrew Gillum has conceded after an ugly battle against a Trumpist conservative, Ron DeSantis.
Meanwhile, Republicans Mike Braun and Kevin Cramer won Democratic-held Senate seats in IN and North Dakota, ousting incumbents Joe Donnelly and Heidi Heitkamp.
Driver was huffing before crash that killed 3 Girl Scouts, mother
A woman with the group and three Girl Scouts - including her daughter - were killed, and a fourth girl was critically injured. The girls were collecting trash next to a rural highway over the weekend when a pick-up truck hit them.
GOP Whip Steve Scalise said the president's rallies were building momentum, and with the economy a selling point, he predicted his party would retain a slim majority.
Cook said Democrats have a possibility of gaining as few as 20 seats and as many as 45 seats.
Democrats also captured governorships in Michigan, Illinois and Kansas.
Trump had aggressively campaigned in the closing days of the race, his focus on boosting Republicans in states that he carried in 2016.
Voters between the ages of 18 and 34 backed Democrats by 62 percent to 34 percent, up from 2014 when 54 percent backed Democrats and 36 percent supported Republicans.
Sanders' interview came before Democrats were projected to win the House, and at that time pointed out that the races were still early.
Trump had fought hard before polling day, crisscrossing the country to claim that Democrats would introduce socialism and making incendiary attacks on illegal immigration that opponents denounced as racist. That leaves a shrunken core dominated by conservatives from rural areas whose constituents overwhelmingly support Trump.
Republicans now have majorities in both chambers of Congress, but polls show that the Democrats are poised to capture the House of Representatives.
Rep. Maxine Waters, who has urged people to get in the faces of Trump administration officials in public could become chairman of the House Financial Services Committee.
With divided leadership in Congress and a president who has taken an expansive view of executive power, Washington could be in store for even deeper political polarisation and legislative gridlock. This is a good sign for Democrats as both groups tend to vote for them.
Investors often favour Washington gridlock because it preserves the status quo and reduces uncertainty, even though many investors this time around had been hoping for a continuation of the Republican agenda.
With control of Congress and statehouses across the nation at stake, numerous nation's top elections were too close to call.