The 2008 United States Senate election in Colorado was held November 4, 2008. The primary elections were held August 12, 2008. Incumbent Republican U.S. Senator Wayne Allard decided to retire instead of seeking a third term. Democratic nominee Mark Udall won the open seat, making this the first time a Democrat won this seat since 1972, and that Democrats held both Senate seats since 1979.

Democratic primary

Candidates

Results

Republican primary

Candidates

Results

General election

Campaign

The election featured an open contest because incumbent U.S. Senator Wayne Allard declined to seek re-election. He honored his 1996 pledge to serve no more than two terms in the U.S. Senate and announced that he would retire from his service to the US Senate and not seek a 3rd term, leaving Colorado's Class II Senate seat open. Both parties believed this senate contest would be one of the most competitive senate races during the 2008 election.

Predictions

Polling

Results

Counties that flipped from Republican to Democratic