Nearly 2.1 million people have cast ballots in a U.S. Senate runoff election in Georgia that will determine whether Democrats control both chambers of Congress.

About 4 million Georgians voted early in the November election, in which Democrat Biden defeated President Donald Trump.

The runoffs pit Democratic challengers Raphael Warnock and Jon Ossoff against Republican incumbents Kelly Loeffler and David Perdue, respectively. The runoff election was necessary because no candidate won more than 50% of the vote on Nov. 3.

More than a quarter of the state’s registered voters have either cast ballots early or through the mail, a sign that turnout in the pair of Senate races will be high, according to state data published Thursday.

The outcome of the race will be critical in shaping Biden’s agenda after he takes office.