Voters line-up to cast their ballots at a polling station in Georgia.
Republicans enjoy a slim 51-49 edge in the Senate and are favored to hang on to their majority since Democrats are defending 26 seats, and Republicans only nine. Typically, the party that does not control the presidency does well during midterm elections, but nothing is determined until the votes come in. "It's you and your accidental two years vs America's first 240 years".
Voter turnout in Pinellas County after the Election Day morning rush is favoring Republicans. "If they abuse those powers they will have no credibility which is a bad result for what they're trying to do", said Henry Waxman, who led Democrats on the oversight committee for over a decade and has been in frequent contact with ranking committee members and House leadership.
Voters line up in Las Vegas.
All 435 seats in the House, 35 seats in the 100-member Senate and 36 of the 50 state governorships were up for grabs.
Democrats are favoured by election forecasters to pick up the minimum of 23 House seats they need for a majority, which would enable them to stymie Mr Trump's legislative agenda and investigate his administration.
Democrats need to gain 23 seats in order to take the House - take a look at vulnerable House seats which Republicans now hold in and around Orange County in California, for example.
Christine Giroux exits the voting booth at Transit Town Hall after casting her vote.
Trump spent election night watching returns with family and friends at the White House, his shadow looming large over the results. "Now it's like the hottest thing".
Early indications would appear to support this.
One in four Americans lives in the 125 congressional districts where no party is widely seen having a lock on Tuesday's vote.
After weeks of bitter campaigning, USA voters go to the polls today. The bill is still being drafted, but Democrats are expecting it to introduce it early in the new Congress.
"They still haven't accepted that they lost the election in 2016", he said. "I have never had to wait that long, ever", Barkley said.
While the campaign has seen intense skirmishes over health care, immigration, education and the best way to share the dividends of high growth, low unemployment and rising wages, Trump has, as he does all the time about everything else, made the campaign about himself.
He claimed Monday that Democrats wanted to make America "a giant sanctuary city for drug dealers, predators, and bloodthirsty MS-13 killers". Appearing in IN, and later in Chicago, Obama warned Democrats not to be distracted by lies and fear-mongering. Despite raising a record amount of campaign cash - $38 million - Beto O'Rourke failed to unseat Republican Senator Ted Cruz.
The message people get, however, will be pretty focused, he said. "No one from outside can stir paranoia or fear that can change that". Independents won some House races, but Democrats won most. You see what's happening with them.
Other tight Senate races are in Arizona, Florida, Indiana, Missouri, Montana, New Jersey, Nevada, North Dakota, Tennessee, and West Virginia. For some, she has become a symbol for dashed hopes in Hillary Clinton's failed presidential bid and a proxy for what could have been. In early voting in Florida, for instance, 40.1 per cent who voted early were registered Republicans, and 40.5 per cent registered Democrats, said media reports. "Today, we say enough".
"We don't know what that caravan is bringing", said Jenkins, who describes Trump as "my guy", though she concedes she cringes at some of what he says.
You may have heard that the "most important election in generations" is happening in the United States this week, and you may have thought to yourself, "but I thought Donald Trump was still in office for another two years?", you're absolutely right.
Yet with several races very close, there is potential for a nail-biting denouement. Democrat and former speaker Nancy Pelosi serves as House minority leader. "When people can just lie with abandon, democracy can't work", he told a cheering crowd as he campaigned for Senator Joe Donnelly.
"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.
That gave President Donald Trump a lot to talk about as he dashed around the country right up to Election Day, campaigning to keep majorities intact.
The governor's races also have far-reaching consequences. Texas has been a mostly Republican state for at least 40 years: Its voters have not backed a Democrat presidential candidate since 1976 and it now has two Republican Senators and a Republican governor.