With a House majority, Democrats will have the power to investigate Mr Trump's tax returns, possible business conflicts of interest and allegations involving his 2016 campaign's links to Russian Federation.
Democratic control of either chamber would also complicate the approval of the renegotiated North American Free Trade Agreement and snuff out any chance of securing funds for a wall on the southern border, which was Trump's signature campaign promise.
The President had dinner with his family and watched the results, which could have a profound impact on the rest of his term and could reshape Washington's balance of power, in the residence of the White House. Moscow denies meddling and Trump denies any collusion.
Trump called the results a "tremendous success", while House Democrat minority leader Nancy Pelosi said "tomorrow will be a new day in America".
"I'm not on the ballot, but in a certain way, I'm on the ballot", Trump said in October.
The election is the culmination of two years of Democratic activism beginning virtually the day after Trump won the 2016 election and officially kicking off with Women's Marches across the country on the day after his inauguration.
Sanders says Trump also called Senate Majority Leader Mitch McConnell "to congratulate him on historic Senate gains".
Down the stretch, Trump hardened his rhetoric on issues that appealed to his conservative core supporters, issuing warnings about a caravan of Latin American migrants headed to the border with Mexico and condemnations of liberal American "mobs".
Speaking on Fox News, Sanders said the candidates that Trump campaigned for are doing well.
The White House for days has been stressing the historical headwinds it faced: In the last three decades, 2002 was the only midterm election when the party holding the White House gained Senate seats. At stake are all 435 seats in the US House of Representatives and 35 of the 100 seats in the Senate.
Fox News hosts Hannity, Pirro join Trump onstage at campaign rally
In 2010, he was ordered not to broadcast his program as part of a Tea Party rally originating from Cincinnati. Fox News said Tuesday that Hannity's appearance was "an unfortunate distraction and has been addressed".
Fears for Russian Federation probe as Trump fires Jeff Sessions
The Justice Department on Wednesday indicated that Whitaker would indeed supervise the Mueller investigation. Mr Trump has at various times belittled Mr Sessions as "beleaguered", "VERY weak", and "DISGRACEFUL".
Los Angeles Chargers release kicker Caleb Sturgis
They looked like a legitimate playoff team and the Seahawks didn't, even though the game was so close . Wilson scrambled for 16 yards to the Chargers 28 and, after a spike, Seattle had 30 seconds left.
In the Senate, centrist Democrats from states that Trump won in 2016 such as Joe Donnelly in IN and Heidi Heitkamp in North Dakota were replaced by conservative Republicans who may credit their victories to the president.
In the state's congressional delegation, Republicans have held 25 of the 36 U.S. House seats.
Some of the campaign's biggest Democratic stars lost.
Their party had put high hopes in flipping the traditionally Republican Texas, but candidate Beto O'Rourke came up just short against incumbent Senator Ted Cruz.
Incumbent Democratic Senator Joe Manchin won a hotly contested race in conservative West Virginia, and conservative Marsha Blackburn held a Senate seat for Republicans.
Democratic gains included several suburban districts eyed for turnover because they were won by Hillary Clinton, including seats outside Washington, Philadelphia, Miami and Denver.
Democrats also captured governorships in Michigan, Illinois and Kansas.
Voting in Chicago, James Gerlock, 27, a Republican, said he wanted to see more of the soaring economic growth that Trump says is the fruit of his business-friendly policies.
The Republican takeover of both houses of Congress in the 1994 election, two years after Bill Clinton's first presidential victory, slowed the Democratic president's legislative agenda.
Allan, the Indianapolis truck driver, said he likes how Trump is leading the country, particularly when it comes to immigration and foreign policy. But the Trump administration's deregulation agenda will likely be protected by officials already in place, which is a positive for the financial sector.