The 2010 United States Senate election in Colorado took place on November 2, 2010, alongside other elections to the United States Senate in other states as well as elections to the United States House of Representatives and various state and local elections. In December 2008, President-elect Barack Obama nominated incumbent U.S. Senator Ken Salazar as Secretary of the Interior. After Salazar resigned from his seat, Democratic governor Bill Ritter appointed Denver Public Schools Superintendent Michael Bennet to fill the seat. Bennet won a full term, defeating former state House speaker Andrew Romanoff in the Democratic primary, and Republican nominee Ken Buck in the general election. With a margin of 1.7%, this election was the second-closest race of the 2010 Senate election cycle after the concurrent one in Illinois.

Democratic primary

Candidates

Nominee

Eliminated in primary

Endorsements

Bennet Romanoff

Polling

Results

[[File:CO-Sen 2010 Dem primary.svg|thumb|Results by county: {{legend|#7996e2ff|Bennet}} {{legend|#7996e2ff|50–60%}} {{legend|#6674deff|60–70%}} {{legend|#584cdeff|70–80%}} {{legend|#1e1dbeff|80–90%}} {{legend|#aade87|Romanoff}} {{legend|#aade87|50–60%}}]]

Republican primary

Candidates

Nominee

Eliminated in primary

Eliminated in convention

Withdrew

Declined

Endorsements

Polling

Results

[[File:CO-Sen 2010 Rep primary.svg|thumb|Results by county: {{legend|#e27f7f|Buck}} {{legend|#e27f7f|50–60%}} {{legend|#d75d5d|60–70%}} {{legend|#D72F30|70–80%}} {{legend|#ff9955|Norton}} {{legend|#ff9955|50–60%}} {{legend|#ff7f2a|60–70%}} Tie {{legend|#AE8BB1|50%}} ]]

Libertarian primary

Candidates

Nominee

Eliminated in primary

Results

General election

Candidates

Major

Minor

Source: Official Candidate List

Campaign

This was one of the most expensive elections in the nation, as more than $30 million was spent by outside organizations. Conservative third party groups hammered Bennet for voting 92% of the time with the Democratic leadership, including voting for healthcare reform and the stimulus package. Liberal third party groups called Buck extremist. Bennet focused on attacking Buck's views on abortion, which he believed should be banned including those of cases of rape and incest. He was also attacked for wanting to eliminate the Seventeenth Amendment and refusing to prosecute an alleged rapist as Weld County district attorney. Planned Parenthood mounted a mail campaign, targeting women voters with the warning that "Colorado women can't trust Ken Buck." Bennet won the women vote by 17 points according to exit polls. After the election, Buck conceded to the Denver Post that the main reason why he lost is because of social issues.

Debates

Predictions

Polling

Fundraising

These totals reflect the campaign accounts of the candidates themselves, and do not include independent expenditures by other groups.

Results

Counties that flipped from Democratic to Republican

Counties that flipped from Republican to Democratic