Donald Trump furiously branded the Georgia runoff results a lie as Republicans looked set to lose at least one senate seat.
The outgoing president took to Twitter to criticise the election as Raphael Warnock appeared positioned to defeat Kelly Loeffler.
“Looks like they are setting up a big ‘voter dump’ against the Republican candidates. Waiting to see how many votes they need?” tweeted Mr Trump.
Democrat Jon Ossoff was locked in a virtual tie with David Perdue with three per cent of the vote in the state left to be reported, though analysts have predicted he will also unseat his opponent.
If Mr Ossoff and Mr Warnock can win both races it will give Democrats control of the senate as vice-president elect Kamala Harris will break all ties once sworn in.
The Republicans need to win just one of the seats in order to give Mitch McConnell control of the high chamber again.
Hundreds of millions of dollars have poured into the state and it is set to be one fo the most expensive elections in US history.
If elected, Mr Warnock will be the first Black senator to serve Georgia and only the 11th ever Black candidate elected to the Senate.
The pastor, who serves the church where Martin Luther King Jr preached, will be one of three sitting Black senators, joining Cory Booker and Tim Scott.
