Before the election, the Democrats had the smallest possible majority in the Senate: 51 of the 100 seats.
But early in the evening, they suffered a defeat when Republican Jim Justice took the Senate seat previously held by Joe Manchin, an independent senator who sided with the Democrats in votes, for West Virginia.
Can swing in the House of Representatives
Later, another seat was lost when Democrat Sherrod Brown was defeated by Republican Bernie Moreno in Ohio.
The Republicans currently have 51 seats in the Senate, while the Democrats have 42. Seven have not yet been decided.
But in the other chamber of Congress, the House of Representatives, the situation may be reversed. The Republicans currently have a weak majority, and have so far secured 189 seats against the Democrats' 165. But if the Democrats win the remaining expected districts, and where representatives are now leading, it will be enough for the smallest possible victory.
Extremely even in some districts
It's a tight race in Montana between Democratic challenger Monica Tranel, a former OS participant, who is leading against incumbent Republican Ryan Zinke. Several tight battles for seats in the House of Representatives are also underway in California, which could determine control of power.
In some districts, the voting is still extremely even – in some cases, less than a percentage point apart.
Congress is the federal legislative assembly in the USA, based in the Capitol in Washington DC. Its work runs in two-year periods, the current 118th Congress meeting started on January 3, 2023. The 119th meeting will be elected on November 5.
Congress consists of the Senate with 100 members, two from each state, and the House of Representatives with 435 seats, distributed in relation to the states' population.
In the Republican-led House of Representatives, there are currently 220 Republicans and 212 Democrats. Three seats are vacant. The even situation and divisions within each party make it difficult to pass laws and budget proposals.
In the Senate, the Democrats have 47 seats and the support of four independent members, giving the party a majority. The Republicans have 49 members.
Sources: USA's Congress, House Press Gallery
