Republicans expanded their Senate majority in Tuesday's U.S. elections, picking up as many as four more seats and knocking off Senate Minority Leader Tom Daschle in the process.

After picking up seats in Georgia, North Carolina, South Carolina and Louisiana, projections show Republicans are assured of at least 55 of the 100 Senate seats, four more than the 51 seats they held before the election.

Republican John Thune's defeat of Daschle in South Dakota marked the first time in 52 years a Senate leader was defeated. Daschle, a three-term senator, was the highest-ranking Democrat in the U.S.

Republican U.S. Senate candidate John Thune at a voting station in Sioux Falls, South Dakota. (AP Photo)

Daschle and Thune both poured money into their quests for votes. Daschle spent about $16 million through mid-October while seeking a fourth term. Thune spent $10 million.

The White House made no secret of its dislike of Daschle, charging him with being the main obstruction to the policies of President George W. Bush.

The Republican party picked up open Senate seats in Georgia, South Carolina, Louisiana and North Carolina. All of those seats were vacated by retiring Democrats.

Illinois U.S. Senator-elect Barack Obama, with his wife Michelle looking on, acknowledges applause from supporters during his acceptance speech in Chicago. (AP Photo)

Thirty-four seats were up for election in total, 19 held by Republicans and 15 by Democrats.

Republican candidate Johnny Isakson easily defeated Democrat Denise Majette in Georgia, after Democratic Senator Zell Miller did not seek re-election.

In a tight race in North Carolina, underdog Republican Richard Burr toppled Erskine Bowles, a chief of staff under former president Bill Clinton, in the race for the seat given up by Democratic vice-presidential running mate John Edwards.

Senator John McCain and his wife Cindy acknowledge the crowd at the Arizona Republican's victory party in Phoenix. (AP Photo)

In South Carolina, Republican Rep. Jim DeMint took the victory.

In Louisiana, Republican David Vitter became the first member of his party since the Civil War to win a term in the Senate.

Republican incumbent Senator Jim Bunning of Kentucky eked out a narrow win over Democratic challenger Dan Mongiardo.

Republican Tom Coburn captured Oklahoma's Senate seat. Coburn, a former three-term representative, had struggled to defeat Democratic Rep. Brad Carson after another Republican senator vacated the post by retiring.

Barack Obama, a rising star who first captured the national eye this summer when he gave the keynote address at the Democratic National Convention, easily won his election in Illinois. Obama will be the only black in the 100-member Senate when it reconvenes in January.

He was the first pickup for the Democrats, who held 48 seats in the current Senate and also have the support of independent Senator Jim Jeffords of Vermont.

Democratic incumbent Senator Patrick Leahy of Vermont won a sixth term and Evan Bayh of Indiana, another Democrat, captured a second.

A Republican incumbent, Senator George Voinovich of Ohio, also easily coasted to his second term.

In Arizona, Senator John McCain was re-elected.