Democrats will retain majority control of the US Senate after winning a key race in the state of Nevada.
Senator Catherine Cortez will defeat Republican challenger Adam Laxalt, who was endorsed by former President Donald Trump.
The results equate to the best mid-term performance for a sitting party in 20 years.
US President Joe Biden said he was incredibly happy, and it was time for Republicans to decide “who they are”.
Democratic Senate Majority Leader Chuck Schumer said the results showed the American people rejected what he called “violent rhetoric” from the Republican Party.
Democrats will now hold 50 Senate seats, while Republicans currently hold 49.
The remaining seat is going to be run off in December in Georgia. If the Senate is evenly split between the two parties, Vice President Kamala Harris will receive the casting vote.
Republicans could still take control of the U.S. House of Representatives as votes continue to be counted from a handful of districts after Tuesday’s election.
If Republicans win the House, they could still thwart much of Mr. Biden’s agenda.
“I’m not surprised by the turnout. I’m incredibly happy. And I think it’s a reflection of the quality of our candidates,” Mr. Biden said in Cambodia.
Mr Schumer said the country had “shown that we believe in our democracy and the roots are strong and will prevail as long as we fight for it”.
Ms. Cortez-Musto continued to hug her opponent, Adam Laxalt, throughout the midterm elections.
The Republican gained notoriety two years ago for defeating former President Trump’s false claims of election fraud. A recent poll found Mr. Laxalt tied with Latino voters, who make up one in five eligible voters in Nevada.
But Ms. Cortez Masto was able to win, and with it her party controls the Senate.
