However, Democrats rode a wave of dissatisfaction with the US President to gain the 23 seats needed to win control of the House.
Millions of Americans voted Tuesday, and results have been projected in several races in the United States midterms, the critical first nationwide election seen as a referendum on Donald Trump's presidency.
In theory, the new Democratic majority would have the capacity to initiate impeachment proceedings against Trump should there be sufficient grounds in Robert Mueller's special counsel investigation.
A simple House majority would be enough to impeach Trump if evidence surfaces that he obstructed justice or that his 2016 campaign colluded with Russian Federation.
Republicans also held on to the only open seat in Tuesday's vote.
Forget for a minute the hot governor's race and the election contest for the U.S. House. Moscow denies meddling and Trump denies any collusion.
It's a messy outcome, with vast consequences for Trump - starting with coping with a House of Representatives controlled by the opposing party.
A Democratic-led House would vote on legislation to block arms deals with Riyadh, make it hard to win congressional approval of a nuclear energy deal and consider a measure to stop United States aircraft refueling and other support for the campaign in Yemen.
Trump had aggressively campaigned in the closing days of the race, his focus on boosting Republicans in states that he carried in 2016.
In the final 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 what he called U.S. liberal "mobs".More news: WWE superstar Triple H tears pectoral muscle at Crown Jewel
Trump in campaign rallies had said that he was on the ballot and made it a referendum on his almost two years rule. Historical patterns and current polling shows the majority party, the Republicans in this case, losing seats during a midterm election. The president was a constant presence on the campaign trail in the last six months, but he rarely stopped by to help House Republicans - an illustration of how intensely unpopular he was in suburban districts across the country, and his decision to train his fire only on motivating hardline base voters to ensure he'd keep the Senate.
The House will now be populated by a rising generation of progressive Democrats, including a record-shattering number of women, a growing group of military veterans and diversity in terms of race, ethnicity and sexual orientation.
The Democrats will be taking back the House of Representatives, multiple news outlets project.
With their majority, Democrats will decide what legislation is considered in the chamber and have a bigger role in setting spending policy and writing legislation. Liberal House member Beto O'Rourke's underdog Senate campaign fell short in conservative Texas against Republican incumbent Ted Cruz.
In a stark illustration of the demographic divides that increasingly define American politics, the Democrats' side of the aisle appears set to be only about one-third white and male, while the Republican caucus is on track to be 90% white men. At the same time, much of the country's deep-red interior got redder, allowing the GOP to easily dispatch Democratic senators in Indiana, Missouri and North Dakota.
After a day of historically high turnout at the polls, Penn students gathered at bars, fraternity houses and dorm lounges to monitor the results of Tuesday's midterm elections.
Democrats turned out to register disapproval of Trump's divisive rhetoric and policies on such issues as immigration and his travel ban targeting several Muslim-majority countries. For the first time in American history, more than 100 women may serve in the 435-member House, at least 28 of them newly elected and representing at least 18 of the districts Democrats flipped. However, Republicans are hoping that this "over-emphasis on the Trump factor" can bring out the president's supporters and give them yet another surprise win, as in 2016 when Mr Trump beat Hillary Clinton. Among those expected: Vice President Mike Pence and former House Speaker Newt Gingrich, an informal adviser to the president.
Republican gains in the Senate are sure to bolster the party's efforts to ram conservative federal judges through confirmation proceedings during a lame duck session that starts next week, as well as next year.
Gridlock in Washington will all but eliminate the potential for more tax cuts, which Trump has called for and which many on Wall Street would like.
Recent months have seen rising internal resistance, with dozens of House Democrats and candidates signalling their desire for change at the top - including Tim Ryan, an OH congressman who challenged Pelosi for the leadership after the 2016 election but fell short.