U.S. Sen. John Hickenlooper on Thursday became the first statewide candidate to submit petition signatures for Colorado’s June Democratic primary, according to his campaign and the Colorado Secretary of State’s Office.

Seeking reelection to a second term, Hickenlooper is facing four primary challengers, led by state Sen. Julie Gonzales, a Denver Democrat. Six Republicans are also running for the seat, including current and former state lawmakers, a county commissioner and a retired Marine colonel.

“We’ve been all over Colorado meeting with voters. Their message has been clear: people feel betrayed by their own president. They want real change in Washington,” Hickenlooper said in a statement.

“We’re honored to have such an outpouring of support,” he added. “We’re not letting up until we flip Congress, rein in the lawlessness of this administration and provide the relief working families are looking for.”

The Hickenlooper campaign said the candidate turned in more than 17,700 signatures, exceeding the required total by more than 5,000. In Colorado, statewide candidates need to gather 12,000 valid signatures from registered voters in their own party, with at least 1,500 from each of the state’s eight congressional districts.

The deadline to submit petitions in order to qualify for this year’s primary is March 18.

While none of Hickenlooper’s primary challengers are circulating petitions, three of the Republicans hoping to make the ballot have pulled petitions: Montrose County Commissioner Sean Pond and first-time candidates Dathan Jones and Amanda Calderon.

The other Republicans running for the office include state Sen. Mark Baisley, R-Woodland Park, former state Rep. Janak Joshi, R-Colorado Springs, and Marine Corps veteran George Markert, making his first run for office.

In addition to Gonzales, the Democratic primary field includes Karen Breslin, Brashad Hasley and Anthony Zimpfer.

Colorado’s U.S. Senate seat is rated solid blue by national election forecasters. State voters haven’t elected a Republican to any statewide office since 2016, and the last time a GOP candidate won one of the state’s two Senate seats was 2010.

Heading into the election year, Hickenlooper held a significant fundraising advantage over Democrats and Republicans seeking to deny him another term.

According to end-of-year campaign finance reports, Hickenlooper raised over $1.1 million in the final quarter of 2025, bringing in more than twice as much as all the other candidates combined.

The incumbent’s nearly $3.9 million cash on hand amounted to more than 10 times as much as the total reported by Joshi, the leading fundraiser among his potential Republican opponents, and was roughly 25 times as much as the sum reported by Gonzales, the top fundraiser among his Democratic challengers

Candidates can make Colorado’s June 30 primary ballot by petition, by going through the caucus and assembly process, or by taking both routes.

Those seeking the nomination at party assemblies must win the support of 30% of delegates, while those who go both routes must clear 10% delegate support at their respective assemblies; otherwise, their petitions won’t count, even if they have enough valid signatures.

Hickenlooper’s campaign wouldn’t say on Thursday whether the candidate intends to seek support at precinct caucuses, which take place next week ahead of the parties’ county, district and state assemblies.

This year, Colorado Democrats are holding their state assembly on March 28 in Pueblo. Republicans have scheduled theirs for April 11, also in Pueblo.

Six years ago, when Hickenlooper won the seat he currently occupies by defeating Republican U.S. Sen. Cory Gardner, the former two-term governor’s campaign also petitioned into the primary and turned in almost exactly the same number of signatures as he did this year. After learning that he’d qualified for the 2020 primary ballot, Hickenlooper announced that he was withdrawing from the assembly process and proceeding to the election.