The 2028 Colorado Senate race will determine who represents the state in the U.S. Senate for a six-year term beginning in January 2029. Colorado currently holds two Senate seats, one of which is up for election in 2028. The state has shifted from a reliably Republican state in the 1990s and early 2000s to a competitive but Democratic-leaning state in recent presidential and Senate elections. The outcome of this race will help determine the balance of power in the Senate, which as of 2025 is closely divided between Democrats and Republicans. Colorado's changing demographics, with rapid population growth in the Denver metropolitan area and along the Front Range, have made it a key battleground for both parties. The 2028 election will be the first Senate race in Colorado since the 2026 midterms, and it will test the political strength of the state's Democratic Party, which has held both Senate seats and the governorship since 2019. The race is also likely to attract national attention and significant outside spending, as control of the Senate may hinge on a few competitive seats. Early speculation centers on whether incumbent Senator John Hickenlooper, who will be 76 in 2028, will seek a second term, and which Republican candidates might emerge to challenge him or run for an open seat. The state's independent and unaffiliated voters, who make up about 48% of registered voters, will be a critical swing group.

Historical Context

Colorado's Senate elections have reflected the state's political evolution over the past two decades. From 1992 to 2004, the state voted for Republican presidential candidates in three out of four elections and had two Republican senators from 2005 to 2009. In 2004, Republican Ken Salazar won an open Senate seat, but he switched to the Democratic Party in 2005. In 2008, Democrat Mark Udall won a Senate seat, giving Democrats both seats for the first time since 1992. The 2010 and 2014 elections saw Republicans regain seats, with Cory Gardner winning in 2014 and Michael Bennet surviving a tough challenge in 2010. The 2020 election was a turning point: Democrat John Hickenlooper defeated Gardner, and Joe Biden won Colorado by 13.5 points. This marked the first time since 2008 that Democrats held both Senate seats and the governorship simultaneously. The 2022 election reinforced this trend, with Michael Bennet winning by 14.8 points. Colorado's population has grown by about 15% since 2010, driven largely by migration from other states, particularly California and Texas. This growth has made the state more diverse and more Democratic-leaning, especially in suburban areas around Denver, Boulder, and Colorado Springs. The state's independent voters have become a decisive force, often breaking for Democrats in recent elections.