A federal judge has struck down a key part of a 2016 ballot initiative that sets a high threshold for Colorado political parties to close their primary elections to unaffiliated voters, delivering a significant win to conservatives within the state Republican Party.
The ruling, in a case filed by the Colorado GOP, did not fully strike down , which opened up primaries to participation by party faithful and unaffiliated voters alike. But in the decision issued on Tuesday, U.S. District Court Judge Philip A. Brimmer wrote that the law puts a “severe burden” on parties that want to opt out of the open primaries.
He ruled that part of the law violates the First Amendment’s protections of the freedom of association.
The law says that if a political party wants to close its primary so that only its own registered voters can participate, 75% of that party’s central committee must vote in support of the change. That threshold is unconstitutionally high, Brimmer wrote.
“The background and origin of the three-fourths opt-out provision is unclear,” Brimmer, who is based in Denver, wrote. “What is clear is that it constitutes an unusual and difficult barrier for the central committee to overcome, more akin to a hurdle to amend a foundational governing document, such as the United States Constitution, than a traditional means of regulating political parties.”
He noted that unaffiliated voters’ share of the Colorado electorate has grown, and they now make up a majority of registered voters in the state.
Brimmer’s ruling does not set a new threshold for parties to hit, should they want to close their primaries, and his order does not give specific direction for how the state or parties should proceed.
The decision also doesn’t appear to impact the upcoming summer primaries. The state GOP meets April 11 for its state assembly, where it will nominate some candidates for those contests, which are set for June 30.
The state GOP filed the lawsuit against the Colorado Secretary of State’s Office in 2023 under the leadership of conservative hardliner Dave Williams. He had blasted Prop 108 as a “radical leftwing” effort and argued that closing the primaries was vital to protecting true Republican candidates.
Representatives for the state Republican and Democratic parties did not return messages seeking comment Wednesday.
Kent Thiry, the millionaire donor who supported Prop 108, criticized what he called a “terrible, tunnel-vision decision” in a statement Wednesday. He said he hoped Brimmer’s ruling would be appealed.
“This decision tramples on the voting rights of a majority of Colorado voters, namely the independent voters,” Thiry wrote. “Voters own elections, not the parties.”
In a statement, the secretary of state’s spokesman John Magnino said unaffiliated voters should be able to vote in primary contests.
“Based on our reading, the court has not disturbed the plans in place for the upcoming June 2026 primary election,” Magnino said. “We are disappointed with this decision and are evaluating next steps in consultation with the attorney general’s office.”
Brimmer previously rejected the GOP’s request to close primaries to unaffiliated voters in 2024, and the lawsuit dragged on for another two years — outlasting Williams and nearly outliving his successor, current GOP chairwoman Brita Horn. Horn is stepping down as party chair later this month.
The new ruling would apply to both the Republican and Democratic parties in future years, should Democrats later choose to close their primaries, too. No party has yet opted out of the primaries under Prop 108’s provision, but Republicans have tried at least three times, according to Brimmer’s ruling.
In September 2023, more than 64% of the party’s central committee who voted on the motion supported closing the primaries, falling well short of the threshold.
The ruling could have far-reaching implications for the state Republican Party, should it choose to close its candidate-selection process only to its own registered voters. The GOP has lost significant ground in the state over the past decade, as Democrats have won control of most statewide offices and secured near-supermajorities in the state House and the Senate.
Still, right-wing conservatives like Williams have argued that the party needs to tack further to the right, even as the state turns deeper shades of blue. Closing state primaries, those figures argue, would ensure that more strictly conservative candidates make it on the ballot, which in turn would activate more Republican voters.
More moderate Republicans, meanwhile, have said the primaries should remain open to unaffiliated voters. In the decade since Prop 108 was passed, an ever-increasing share of voters has registered as unaffiliated, and moderates contend that the party should be as open to the state’s changing voter base as possible.
Brimmer wrote that roughly 100,000 unaffiliated voters participated in Republican primaries in 2018. By 2022, that total had more than doubled to 231,000, accounting for 37.1% of ballots cast in those contests that year. In some counties, the unaffiliated voters rivaled the number of Republican voters participating in the GOP’s primaries in 2022 and 2024.
