Mitt Romney, the 2012 Republican presidential nominee, has won election to US Senate from Utah, as expected.
In an unusual twist, Trump was brief in his comments after Republicans lost the House.
The GOP Senate victory was magnified because Democrats stood a solid chance of wresting control of the House from Republicans.
The path of least resistance for Democrats to a majority in that chamber led through educated suburban districts that had long voted for Republicans, but contained voters that may have been uneasy with Donald Trump's policies and rhetoric. While many Democrats called for a bipartisan change in leadership on the campaign trail, fewer than a dozen who won on Tuesday night guaranteed they'd vote against Pelosi, leaving her the tiniest bit of a cushion to become Speaker even as she loses some votes.
Problems with voting machines prevented Americans from casting ballots in a dozen states, USA rights advocates said, following complaints about registration problems, faulty equipment and intimidation they have received throughout early balloting.
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.
In the leadup to the election, Republicans privately expressed confidence in their narrow Senate majority but feared the House could slip away.
"Even though they won back the House, they're going to have to decide whether they ought to advance as a more Elizabeth Warren, Bernie Sanders type of party with more liberal positions, or as a more center-left party", Gergen said.More news: First two Muslim women elected to US Congress: networks
While Deb Haaland in New Mexico and Sharice Davids in Kansas are the first two Native American women in Congress.
Almost 40 percent of voters cast their ballots to express opposition to the president, according to AP VoteCast, a national survey of the electorate, while about 25 percent said they voted to express support for Trump.
Both parties' closing messages appeared to have animated their respective bases, according to VoteCast, with health care and immigration each described as the most important issues in the election by about 25 percent of voters. "Certainly we feel good about where things are headed".
But nonetheless, Republicans have been bracing for a loss in the House, though they anticipate keeping ahold of the Senate.
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.
Still, nearly 7 in 10 said the economy was in good shape, and those who said their personal finances were in better shape now than two years ago outnumbered those who believed their finances were worse off, according to the polling.
With control of the House, Democrats will chair powerful committees and have subpoena power to seek Trump's tax returns and more aggressively investigate Russian interference in the 2016 election and whether there was any collusion by the president's campaign.
"The President has energized a staggering number of Americans at packed arenas and in overflow crowds at rallies across the country", Sanders said.
Yet Democrats' dreams of the Senate majority as part of a "blue wave" were shattered after losses in Indiana, Tennessee, North Dakota and Texas.
"All day it felt like today like America was in the doctor's office waiting for our STD results to come back", Jimmy Kimmel said on his live Kimmel Live. The GOP's grip on high-profile governorships in Florida, Georgia and Wisconsin were at risk as well.