Democrats had strong nights in both the Midwest/Rustbelt region and in the Southwest part of the U.S., the regions of the country which will decide the 2020 presidential election.
With the Republicans keeping control of the Senate, the outcome in the House could mean gridlock for Trump's agenda on Capitol Hill - or, conversely, it could open a new era of deal-making. Trump also held out an olive branch to Pelosi, 78, a former Speaker who is a front runner for the job, but who is opposed by more than 50 members of her own party who want a fresh face and younger blood to lead them.
But Republican voter James Gerlock, 27, said he wanted to see more of the soaring economic growth that Trump says is the fruit of his business-friendly policies.
The 2018 elections also exposed an extraordinary political realignment in an electorate defined by race, gender, and education that could shape USA politics for years to come.
The GOP's successes were fuelled by a coalition that's decidedly older, whiter, more male and less likely to have college degrees.
After all, the strong turnout among Democrats during the primaries suggested a more motivated base than their Republican rivals.
Democrats boasted record diversity on ballots.
Dennis Hof, Recently Deceased Brother Owner, Wins Nevada Election
This year, he ran as a Republican and earned backing from Trump associate Roger Stone and tax-cut activist Grover Norquist . Arguably the single biggest victor in the US Midterms is a brothel owner who has been elected as a congressman for Nevada.
In suburban areas where key House races were decided, female voters skewed significantly toward Democrats by a almost 10-point margin.
"I am so honoured to share both the ballot and the stage with the many visionary, bold women who have raised their hand to run for public office", said Ayanna Pressley, who became the first black woman elected to Congress from MA.
Three candidates had hoped to become their states' first African-American governors, although just one - Georgia Democrat Stacey Abrams - was still in the running.
In suburban areas where key House races will be decided, voters skewed significantly toward Democrats by a almost 10-point margin.
Democrats celebrated a handful of victories in their "blue wall" Midwestern states, electing or re-electing governors in Michigan, Pennsylvania, Minnesota and in Wisconsin, where Scott Walker was defeated by the state's education chief, Tony Evers.
Democrats knocked off at least 17 GOP incumbents, picking up moderate, suburban districts across the country.
The law Democrats would use to demand the tax returns was created during the Teapot Dome scandal in the Harding administration, when lawmakers were investigating conflicts of interest during the White House at that time. Many of those incumbents retired in part because of Trump.
Actually, you can and do if you're like most Democrats and never-Trump Republicans.
Democrats 'take control' of House
In one result that did not come as a surprise, former Republican presidential nominee Mitt Romney won a Senate seat in Utah. While these were the first two districts to flip, Democratic leaders had appeared positive throughout the day on Tuesday.
If Democrats demand the returns and Mr Trump refuses to release them, it could set off a series of legal challenges, with federal judges being asked to adjudicate the limits of the President's power. In his only public comment on Tuesday night, he tweeted: "Tremendous success tonight".
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.
Some hurt worse than others. And they would claim subpoena power to investigate Trump's personal and professional shortcomings.
Democrats were most optimistic about the House, a sprawling battlefield set largely in America's suburbs where more educated and affluent voters in both parties have soured on Trump's turbulent presidency, despite the strength of the national economy. "Two can play that game!"
The president bet big on a xenophobic closing message, warning of an immigrant "invasion" that promised to spread violent crime and drugs across the nation.
For the past two years, White House lawyers and the Trump Organisation have repeatedly rebuffed Democratic efforts to get even the most basic financial information on Trump's businesses.
As for the Senate race, despite Trump's deeply polarizing effect on voters, the GOP harnessed his rock-solid popularity with hard-right voters in rural, deep-red states. The loss of 26 seats in the House, meanwhile, is dwarfed by the 63 seats lost by President Barack Obama in 2010 and the 52 seats lost by President Bill Clinton in 1994. Democrats won seats stretching from suburban Washington, New York and Philadelphia to outside Miami, Chicago and Denver.
In a string of rallies attracting thousands of supporters in battleground states and districts, Trump leant heavily on his anti-immigration views, portraying a caravan of central-American migrants as a dire threat, and the other party as pandering to illegal immigrants.
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