The first national elections since Trump captured the White House in a stunning 2016 upset will be a referendum on the polarising Republican president and his hardline policies, and a test of whether Democrats can turn the energy of the liberal anti-Trump resistance into victories at the ballot box.
Democrats will have around 229 seats in the 435-member House, while Republicans will hold 53 seats in the 100-member Senate, up from 51, according to projections by The New York Times.
Mr Trump hailed "tremendous success" and an "incredible day" for his party in Tuesday's elections.
"Now is the time for members of both parties to join together, put partisanship aside, and keep the American economic miracle going strong", Trump said. They talked on election night about doing an infrastructure package and lowering health care costs, particularly around prescription drugs, priorities for both sides. But, he warned, he will respond in kind and government will suffer.
Democrats are divided over which candidate, strategy and vision can forge a coalition capable of defeating Trump in two years. "All you are going to do is end up in back and forth and back and forth". "I'm proud of what happened".
Of the special counsel's Russian Federation investigation that has shadowed his administration for more than 18 months, Mr Trump said that he could end it now but lets it continue.
New Jersey senator Bob Menendez, addressing the crowd in Hoboken after his re-election victory, said he was told that the state's junior senator, Democrat Cory Booker, "may be busy really soon".
Trump sparred with reporters at the post-election news conference, ordering several to sit down and telling CNN's Jim Acosta he was a "rude, terrible" person and "enemy of the people".More news: Indonesian Plane Grounded as Passengers Refuse to Fly Because of Durian Fruit
In ill-tempered exchanges, he called a CNN correspondent "a rude, awful person" and told an NBC reporter: "I'm not a big fan of yours either".
"At the end of the day, ME people don't care which party you identify with, they just want someone who is honest, believes in our state and vows to do what they say they'll do", Jackson said.
Trump's Republicans lost the House of Representatives in Tuesday's vote but increased their majority in the Senate.
With winners called in all but one statewide race, Republicans were on pace to gain three seats in the Senate and defended their lead in governorships by a two-seat margin.
He singled out GOP Representatives Mike Coffman of Colorado, Mia Love of Utah, Barbara Comstock of Virginia, Carlos Curbelo of Florida, Peter Roskam of Illinois, Erik Paulsen of Minnesota, John Faso of NY and Bob Hugin, who challenged Senator Bob Menendez of New Jersey.
Beyond trying to get their hands on the Holy Grail of President Donald Trump's business dealings - his tax returns - House Democrats are prepared to use their newfound majority and subpoena power to go after all manner of financial records that could back up their claims that he's using his presidency to enrich himself and his family.
Trump offered an olive branch to House Democrats as an alternative to an investigative face-off. "And if it becomes clear that this is another move to shut down the Mueller investigation, then that is something that we'll have to seriously consider".
But Trump returned to his main message when asked what his key takeaway was from the midterm results. The 30-second spot featured courtroom video of an illegal immigrant from Mexico convicted in the 2014 killings of two police officers, juxtaposed with scenes of migrants headed through Mexico. "But what we stand for meant a lot to most people".
But without overwhelming numbers, Democrats will not have the strength to push numerous initiatives their left flank ran on: a single-payer health care system, boldly expanded college access and an Immigration and Customs Enforcement agency that is at least reined in.