The Democrats in the House have won 218 seats, and the Republicans have 201; 16 seats have still not been called as the electoral process is still ongoing. For a majority in the House, 218 seats are needed. Democrats have managed to keep the majority in the House.
The Senate race is still up in the air. For Republicans to keep their majority, they need to have 51 seats, whereas the Democrats only need 50 seats, since the tie-breaker is the Vice-President. Currently, both parties have 48 seats, and 4 are yet to be called. There are two senate run-offs which will decide these seats, on January 5th, in Georgia and will ultimately decide the balance of power in Washington.
If the Democrats were to win a Senate majority, their control of the House, the Senate, and the Presidency would mean they have substantial power in Washington to pass legislation.
However, if they were to lose the Senate, majority leader Mitch McConnell, a Republican Senator from Kentucky, would hold the power to halt Biden’s legislative agenda.
The Senate race could prove detrimental for US’s foreign policy. Although the Constitution gives the President power to make treaties, the president must submit them to the Senate and get a two-thirds approval vote. Additionally, the president has the power to nominate ambassadors and appoint the Secretary of State, but needs consent from the Senate. The State Department is responsible for creating and implementing the President’s foreign policy.
Biden will not need the Senate’s approval for rejoining the Paris Climate Change Agreement, or for rejoining WHO, which he has vowed to do at the start of his term.