Incumbent Sen. John Hickenlooper (D) defeated Julie Gonzales (D) in the Democratic primary for the U.S. Senate in Colorado on June 30, 2026.

Ahead of the primary, Colorado Politics' Thelma Grimes wrote that "Gonzales is running on a message of generational change, arguing that Democrats need a more aggressive approach and that a vote for Hickenlooper will just mean 'more of the same.' Hickenlooper, a fixture in politics for decades, is campaigning on experience and stability, highlighting his work in the U.S. Senate and his record as Denver's mayor and Colorado governor."

Hickenlooper was elected to represent Colorado in the U.S. Senate in 2020. He previously served as governor of Colorado from 2011 to 2019 and mayor of Denver from 2003 to 2011.

According to Hickenlooper's campaign website, "Just like he's done throughout his career, he will use his independent perspective to bring people together to get things done — from lowering health care and prescription drug costs to keeping our families safe from gun violence, as well as protecting the state's public lands while combating climate change." Sen. Elizabeth Warren (D-Mass.), Brady PAC, and End Citizens United PAC endorsed Hickenlooper.

Gonzales was elected to represent District 34 in the Colorado Senate in 2018. She previously worked as a community organizer.

According to Gonzales' campaign website, "She's candid about the reality families face today: too many people are working just as hard without getting ahead because the rules are tilted toward the wealthy and well-connected. That's why she's running a people-powered campaign to lower costs, protect fundamental freedoms, and make sure Colorado is a place where every family can afford a home, see a doctor, and build a future with dignity." Colorado AFL-CIO, Colorado Working Families Party, and Our Revolution endorsed Gonzales.

Hickenlooper and Gonzales took different approaches to get on the ballot.

Hickenlooper went through the petition process, in which he needed to collect 1,500 verified signatures per congressional district. On March 24, 2026, the Colorado Secretary of State's Office verified that Hickenlooper met that threshold.

Gonzales went through the assembly process. In Colorado, parties conduct county, district, and state-level assemblies to designate candidates for the primary election ballot. These assemblies are composed of delegates selected at local precinct caucuses.

During the assemblies, a candidate must receive at least 30% of the votes cast. If that does not happen on the first ballot, a second ballot is held. If no candidate receives at least 30% on the second ballot, the top two vote-getters make the ballot. In the Colorado Democratic Party's 2026 statewide assembly, Gonzales won 74.4% of the vote on the U.S. Senate ballot, Karen Breslin (D) won 24.3%, and Jessica Williams (D) won 1.2%. Since Hickenlooper did not participate in the assembly, delegates could not vote for him.

As of June 30, 2026, The Cook Political Report with Amy Walter and Inside Elections with Nathan L. Gonzales rated the general election as Solid Democratic. Larry J. Sabato's Crystal Ball rated it as Safe Democratic.