The Republicans have kept control of the Senate, with several races still to be decided.
Senator Pat Toomey’s narrow victory over Democrat Katie McGinty, in Pennsylvania, pushed the party over the line.
It means the Republicans will continue to have control of both Houses of Congress.
Republican Donald Trump has also edged closer to winning the White House with a series of shocking wins in battleground states such as Florida and Ohio on Tuesday.
If Donald Trump wins the White House, the party will have a clean sweep, making it easier for them to pass legislation.