WASHINGTON (AA) – Democratic Sen. Raphael Warnock from the US state of Georgia and Republican challenger Herschel Walker are headed for a run-off election after neither candidate received a clear majority, according to an Associated Press projection on Wednesday.

The contest is increasingly pivotal in determining which party will lay claim to the 100-member Senate. Currently, Republicans hold 49 seats in the chamber, compared to 48 for Democrats. Three races, including in Georgia, remain outstanding.

Warnock and Walker will head to a Dec. 6 run-off election, this time without Libertarian candidate Chase Oliver who appears to have received about 2% of the vote.

Control of the Senate and the House of Representatives remains very much in question.

Earlier Wednesday, Sen. Ron Johnson won reelection in the state of Wisconsin, according to an Associated Press projection. The race was called hours after Democrats flipped a key Senate seat in the state of Pennsylvania as they seek to claim an outright majority in the chamber.

The Pennsylvania seat had been tightly contested between victorious Lt. Gov. John Fetterman and Republican celebrity doctor Mehmet Oz, but Fetterman claimed victory early Wednesday. Oz conceded shortly thereafter.

Critical races in Arizona, and Nevada have yet to be called.

Democrats need 50 seats to hold a Senate majority thanks to Vice President Kamala Harris, while Republicans would need 51 since their party does not currently hold the White House.

An American vice president serves as president of the Senate and is able to cast tie-breaking votes. Senate tradition has held that control of the chamber in an evenly-split body goes to the party that controls the White House.

Republicans have been projected to win 204 of the 435 seats in the House of Representatives. Democrats, meanwhile, have won 176, according to The AP. Either party needs to claim 218 seats to win a majority.

In addition to all 435 House seats, there are 35 seats in the Senate that are up for grabs in the chamber as well. The vast majority of contested Senate seats, 21, were held by Republicans this election cycle. One-third of all seats in the chamber go up for election every six years, while all House seats are contested every two years.

If Republicans win the House, as is likely, President Joe Biden’s legislative agenda will be almost certainly stopped in its tracks, facing an uncooperative Republican-dominated body.

If Republicans also take control of the Senate, Republicans could also block or slow down many of Biden’s appointments to key administration positions, as well as federal judges, who enjoy lifetime appointments, helping to shape public life for decades.