Women hold 23 of the 100 U.S. Senate seats, and this year 23 women are on the ballot for the chamber.
In states without super competitive races, Trump's approval tends to be either much higher or much lower.
Democrats quickly made important gains in the House, but Republicans defended in crucial races, like incumbent Andy Barr of Kentucky, whose House seat had seemed at risk. But each of these possibilities have been accounted for in pollsters' projections that there is a six in seven chance that Democrats will take back the House - so I'd say it's pretty likely this is what will happen.
Voting will close in another 18 states at 8pm.
Without mentioning President Donald Trump by name, Shalala had a clear message for the White House in her victory speech.
By 11:30 p.m. Eastern, ABC was reporting Democrats had won 209 seats and Republicans 190 had been elected to the House, making it clear that there would be no "blue wave" as Democrats had been promising for months.
U.S. citizens will vote to select their preferred members of Congress, both for the House of Representatives and for the Senate, as well as state Governors and down-ballot positions such as local representatives and judges.
The volatile midterm campaign was marked by clashes over race, immigration and trade. More self-identified Democrats than Republicans headed to the polls this year (37 to 33 percent).More news: Apple Products Come with Revised Prices for India Market
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The expectation is that Democrats will bring a new level of oversight and investigation of the Trump administration, but numerous candidates ran on issues like healthcare and immigration.
Democrats were gaining speed in their quest for the House, which would give them the ability to launch investigations into the president and stymie his agenda. Republican Sen. Cindy Hyde-Smith and Democrat Mike Espy advanced to a November 27 runoff election.
But Democrats have been fired up by anger at Trump's extraordinary attacks over the last few weeks against immigrants, claiming that his opponents seek to throw open the borders to "drug dealers, predators and bloodthirsty MS-13 killers".
USA stocks opened flat on Tuesday as investors awaited the election results. Around 57% said they approve of the job he's doing, fitting with the positive news for Republicans as CNN predicts Republican Marsha Blackburn will take a US Senate seat. "I remember coming out of the White House one day in August and realizing it was the first time I'd been outside when the sun was still up in a long time", said Democratic strategist Chris Lehane, who worked in the Clinton administration during the Whitewater scandal. "Who we are is on the ballot", he said.
He estimated turnout would reach 45 percent; that would be the highest for a midterm election in 50 years. In the last such congressional elections in 2014, there were 27.5 million early votes.
In the Senate, where Democrats were defending seats in 10 states that Trump won in 2016, Republicans ousted four incumbent Democrats: Bill Nelson in Florida, Joe Donnelly in Indiana, Heidi Heitkamp in North Dakota and Claire McCaskill in Missouri.
Trump has framed the elections as a choice between law and order maintained by Republicans and an out-of-control Democratic mob, while focusing heavily on hardline immigration campaign promises, including a legally dubious pledge to end birthright citizenship for the children of undocumented immigrants born in the US.
Mr Trump is not up for re-election until 2020, but Tuesday's vote was seen as a referendum on a polarising president.
"Most [Democratic candidates] were talking about the fact that if Donald Trump is in charge, Americans who have preexisting conditions or any kind of health challenge for themselves or their family, won't be able to buy health care", he said.