It is common for the midterms to go poorly for the party with an incumbent President, but losing the House will still come as a huge blow to Trump, after campaigning relentlessly over the past couple of months.
Nadler could become chairman of the House Judiciary Committee, and the New York Times teased that Nadler "could bring the president serious pain and potentially oversee his impeachment".
Nearly a quarter of voters considered immigration to be the top issue, while another one-fifth said it was the economy. More women than ever were running, along with veterans and minorities, many of them motivated by revulsion over Trump. If he is successful, he would become the first Democrat elected to the Senate in Texas in three decades.
With a House majority, Democrats will have the power to investigate Mr Trump's tax returns, possible business conflicts of interest and allegations involving his 2016 campaign's links to Russian Federation.
Americans are voting for all 435 seats in the House and 35 out of 100 seats in the Senate, a as well as state governors.
Polls indicated that Democrats have a good chance of winning the 23 seats they need to seize the House, while Republicans could slightly increase their razor-thin Senate majority of 51-49.
Pollsters, gun shy after getting their 2016 presidential prediction wrong, urged caution.
"Thanks to you, tomorrow will be a new day in America", Democratic House leader Nancy Pelosi told cheering Democrats at a Washington victory party, saying House Democrats would be a check on Trump.
Said White House counsellor Kellyanne Conway, "I don't know that there will be much of an appetite for Democrat lawmakers to spend all of their time, or most of their time or even a fraction of their time investigating, instigating, trying to impeach and subpoena people".
Voters often sit out the midterms. About 40 million early votes were likely to be cast, said Michael McDonald, a professor at the University of Florida who tracks the figures.
Maybe the "blue wave" turned out to be a "blue ripple", Seth Meyers said on Late Night, "but hey, if you've been in the desert for two years, a little splash of water feels like a damn tsunami".
In Snellville, a rural town in northern Georgia, people said that the line to vote at Annistown Elementary School was hours long because of problems with voting machines.
In a big change from previous midterms, just 1 in 5 voters said the economy was the most important issue in the election this year - even though Trump sought to make that the center point of his effort to push Republicans."Now it's like the hottest thing".
With a jam-packed rally schedule and a spirited message to his supporters, Trump made the first election since he captured the White House in 2016 a referendum on his agenda. The Republican incumbent had been branded Barbara "Trumpstock" by Democrats in a race that pointed to Trump's unpopularity among college-educated women in the suburbs.
"I am extremely happy with the economy", Gerlock said.
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.
Trump has sent soldiers to the Mexican border, threatened to have illegal immigrants shot if they throw stones at the border, and vowed to restrict citizenship rights.
"With Democrats' leadership in the state solidified, NY can pass policies previously blocked by Republicans to expand health care coverage, address climate change, and ensure women retain the right to make their own medical decisions", Jessica Post, executive director for the Democratic Legislative Campaign Committee, said in a statement on Tuesday.