The 2008 United States Senate election in Delaware was held on November 4, 2008. Incumbent Senator Joe Biden, who was also the Democratic nominee for vice president in the concurrent presidential election, faced Christine O'Donnell in the general election. Biden won re-election to a seventh term with 64.69% of the vote, his best-performing result in his senatorial career, while also being elected vice president. Biden took his oath of office in the Senate chamber with the rest of his colleagues on January 3, 2009, but resigned his seat on January 15, 2009, and assumed the vice presidency five days later. Delaware Governor Ruth Ann Minner appointed Ted Kaufman, a Democrat and longtime Biden advisor, to fill the vacant seat pending a 2010 special election in which O'Donnell once again ran unsuccessfully for the seat, losing to Democrat Chris Coons. This marked the last time Biden won all three counties in the state, as concurrently in his vice presidential runs in 2008 and 2012, and in his presidential run in 2020, he would go on to only win New Castle and Kent counties, as Sussex County would vote for the Republican ticket in each election.

Candidates

Democratic

Republican

General election

Campaign

After ending his 2008 presidential bid in January 2008, Biden focused instead on running for a seventh Senate term. He was unopposed within his party. O'Donnell faced businessman Tim Smith at the Republican state party convention and won with more than 60 percent of the delegate vote. On August 23, 2008, Democratic Party presidential nominee Barack Obama announced that he had selected Biden to serve as his vice presidential running mate. Under Delaware law, Biden could run simultaneously for both his Senate seat and for vice president, which he decided to do. The statewide party primary elections were held September 9, 2008. O'Donnell was uncontested in the Republican primary, as was Biden in the Democratic primary. O'Donnell tried to make an issue of Biden's dual campaigns, claiming that serving his constituents was not important to him, and criticized his unwillingness to participate in debates and candidate forums. Nevertheless, she was heavily outspent by Biden and her campaign failed to gain traction. Her campaign ended with $23,000 in debt. Minutes after the polls closed on November 4, NBC called the race for Biden, with other news organizations soon following.

Predictions

Polling

Results

County results

Counties that flipped from Republican to Democratic