Senate Democrats faced a steep challenge as they fought to keep seats in states Trump won by double-digit margins in the worst battlefield for any party in modern history.
The midterms also featured some potentially historic candidates, including Stacey Abrams, who would be the first black woman to be governor of Georgia if she won. Several television networks, including the president's favorite Fox News Channel, yanked a Trump campaign advertisement off the air on the eve of the election, determining that its portrayal of a murderous immigrant went too far.
Mucarsel-Powell ousted Republican Rep. Carlos Curbelo from the District 26th seat.
Should he conclude that Trump committed a crime, a Democratic House could launch impeachment proceedings, but the process would likely come to a halt in a GOP-held Senate. The party has pledged to check the president's power and start a slew of investigations on matters including his tax returns, Russian involvement in the 2016 election and actions by his administration.
Goodstein, however, still believes that Trump "is uniquely disfavored" and numerous voters who strongly disapprove of Trump will take to the polls, allowing the Democrats to regain the House of Representatives.
Trump was not on the ballot this year but he has been an unmistakable force in congressional contests and statewide elections across the country.
"They (Republicans) have been trying to take Medicare away form us, our medical services, and it's important that we vote for candidates who will defend that", he said at a polling place in Tornillo, Texas.
Democrats, whose very relevance in the Trump era depended on winning at least one chamber of Congress, were laser-focused on health care as they predicted victories that would break up the GOP's monopoly in Washington and state governments.
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Health care and immigration were high on voters' minds as they cast ballots in the midterm elections, according to a wide-ranging survey of the American electorate conducted by The Associated Press. This small error, along with the fact that some undecided voters unexpectedly voted for Trump, handed him the electoral college.
A group of women register to vote in front of the San Diego Registrar of Voters building on November 6, 2018.
Ballot counting could drag in tight races, leaving some races undecided long after Election Day.
But several of those states contain key races that will offer the first indications on whether Democrats have the momentum to take the House or if Republicans are performing more strongly than expected. Young voters promised to vote in record numbers as they waged mass protests in the wake of the February mass shooting at a Parkland, Florida, high school that left 17 students and staff dead. At least three other red districts flipped to blue.
Ms. Comstock would be the first GOP casualty of the night, losing her district in suburban Washington. Claire McCaskill of Missouri, likely the Democrat speaking most aggressively about taking on the pharmaceutical industry, lost her race in Missouri.
In the final days of the campaign, Trump amped up his rhetoric, peppering his rallies with improbable doomsday scenarios should the Democrats win control of one or both congressional bodies.
The Senate GOP Conference's leadership ranks are not expected to change much. Ted Cruz held off Democrat Beto O'Rourke. Democrats also captured governorships in MI and IL.
The committee also distanced itself from eight-term Rep. Steve King of Iowa after racial remarks, and his seat was unexpectedly contested in the final week of the campaign.
All 435 seats in the US House were up for re-election, although fewer than 90 were considered competitive. Thirty-three incumbent Republicans plan to retire from the House after their current term.
White House spokeswoman Sarah Sanders said Trump planned to spend Election Day making phone calls and monitoring the races from the White House, and would watch the results later with family and friends.