Democrats have held onto their majority in the US House of Representatives, while the control of the Senate remains undecided.
According to tallies by some major U.S. media outlets, Democrats have won at least 218 seats in the 435-member chamber as of Tuesday, while Republicans have taken 201, as more than a dozen races have not yet been called.
Meanwhile, Republicans have flipped a net six seats, narrowing Democrats' advantage in the lower chamber.
Nancy Pelosi, the top Congressional Democrat, has announced that she's seeking to be reelected as House speaker.
Thirty-five seats were up for grab in the 100-seat Senate this year. With three races still undecided, the Republicans are leading with 49 seats compared to 48 for the Democrats.
Mitch McConnell of Kentucky was reelected as Senate Republican leader on Tuesday, while Chuck Schumer of New York was picked again to head the Democratic caucus.
In the White House race, Democrat Joe Biden has declared victory and rolled out a presidential transition, while sitting President Donald Trump hasn't conceded and is mounting challenges in court over allegations of voter fraud and counting misconduct.
Biden has clinched at least 279 electoral votes, according to projections by U.S. networks. To win the White House, a candidate needs at least 270 electoral votes of the 538 in total.
After the election, each state has its legal deadline for certifying results, a process that frequently takes a few weeks and generally starts with counties certifying results to the state.
A federal law sets what is called the "Safe Harbor" deadline, falling on Dec. 8 this year, the day by which states must submit the winner of the presidential election if they are to be insulated from legal disputes.
Electoral College representatives will meet six days later, on Dec. 14, to formally select the next U.S. president.
The U.S. Congress will meet in joint session to count the electoral votes on Jan. 6 next year. The inauguration Day is Jan. 20.