The Republicans retained control of the Senate for another two years, destroying the Democrats' dreams of an anti-Trump wave sweeping them into a majority.
The result was almost certain when Republican Kevin Cramer ousted North Dakota Democratic Senator Heidi Heitkamp and republican businessman Mike Brown, Senator Joe Donnelly, in Indiana.
In the meantime, Ted Cruz resisted the spirited challenge of Democrat Beto O'Rourke and Republican Senator Marsha Blackburn in Tennessee.
The profits of the Republicans were added when the results in Nevada and Arizona are not yet known
Donald Trump spoke of a "tremendous success" in a post on Twitter.
In the meantime, Democrats gained ground in the fight for home control and won half the seats they needed. Dozens of other competitions were still available.
Victories in contested house races in Florida, New York, Virginia, Pennsylvania and Minnesota gave them cause for optimism.
The mixed results that unfolded as a concerned nation watched as voters reward or reject Republicans at the first nationwide election of Mr. Trump's turbulent presidency.
Great success tonight. Thanks to all!
– Donald J. Trump (@realDonaldTrump) November 7, 2018
In the run-up to the elections, the Republicans privately expressed their confidence in their tight Senate majority, but feared that the house could slip.
The influence of Republicans on prestigious governorates in Florida, Georgia and Wisconsin was also threatened.
"Everything we've achieved is at stake," Trump said on his last day of election.
Long queues and faulty machines have affected the first hours of voting in some districts, including Georgia, where some voters said they had waited up to three hours to vote in a hotly-contested gubernatorial election.
More than 40 million Americans had already voted, either by e-mail or in person, and, according to the analysis, early broke votes in 37 states.
According to a national poll among voters, nearly 40% of voters vote to speak out against the president. One in four respondents said they had voted in favor of Mr Trump.
Mr. Trump encouraged voters to see the country's first nationwide election of his presidency as a referendum on his leadership, and proudly pointed to the emerging economy at recent rallies.
Vote Red 🇺🇸 MAGA 🇺🇸 https://t.co/i95OiBimxA pic.twitter.com/ncvDcAP8LZ
– Melania Trump (@FLOTUS) November 6, 2018
He backed on a xenophobic final message and warned against an "invasion" of immigrants who promised to spread violent crime and drugs across the country.
The Democrats had to take two dozen seats to reach the majority of the house, and two seats to control the Senate.
All 435 seats in the US House were available for re-election, though less than 90 were considered competitive, while about 35 senate seats were in play, as were nearly 40 governorship offices and the balance of power in virtually every state legislature.
The political and practical missions were sky-high.
Democrats could derail Mr Trump's legislative agenda for the next two years if they gained control of the house.