Bennet's main challenger was Republican nominee Darryl Glenn, an El Paso County commissioner.

Senator Ken Salazar resigned in January 2009 to become United States Secretary of the Interior and Governor Bill Ritter appointed Bennet, the Superintendent of Denver Public Schools, to replace him.

[7] Robert Blaha, Jack Graham, Jon Keyser, and Ryan Frazier sought to qualify for the ballot by petition instead of through the State Assembly.

[12] In early June, when asked by a fellow Republican candidate and a retired air force lieutenant colonel whether Keyser received his Bronze Star for work on a software program or for "kicking in doors" in combat as "represented to the community", Keyser refused to answer the question and claimed he had "no idea" what software program his rival was talking about.

[13] [14] In August 2014, Republican candidate Jack Graham was fired as Colorado State University Athletic Director for reasons that were not specified, though he would continue to be paid through the November 2016 election.