A federal judge ruled March 31 that Proposition 108’s requirement — 75% of a major party’s state central committee must vote to opt out of the semi-open primary — violates the First Amendment. The ruling does not affect the June 2026 primary, but it opens a path for Republicans to close their primaries to unaffiliated voters as early as 2028.
U.S. District Judge Philip A. Brimmer found the threshold “constitutes a severe burden on the major parties’ right to association and is therefore unconstitutional.” He compared it to “a hurdle to amend a foundational governing document, such as the United States Constitution, than a traditional means of regulating political parties.” Brimmer applied the Anderson-Burdick balancing test and concluded the state could not justify the burden.
The Colorado Republican Party has tried five times since 2017 to opt out. Every recent attempt drew majority support from members present, but none reached 75%. In September 2025, 226 central committee members voted to opt out — a majority of those present. That number represented only 44.57% of total membership.
Unaffiliated participation in Republican primaries has grown sharply. In 2018, roughly 100,000 unaffiliated voters cast ballots in GOP contests. By 2022, that number reached 231,000. Unaffiliated ballots accounted for 37.1% of all Republican primary votes statewide that year.
In Denver County’s 2024 presidential primary, unaffiliated voters outnumbered Republicans by more than 9,000. More than half of Colorado’s four million active voters are now unaffiliated. Republicans account for roughly 942,000. A party-commissioned survey found the two groups “do not share a common identity or set of political values or ideologies.”
Brimmer did not strike down Proposition 108 entirely. The party could not identify a single nonpresidential primary where unaffiliated voters changed the outcome, and Brimmer acknowledged no demonstrated electoral harm. But he found the growing proportion of non-member participation creates a constitutional burden, and that the 75% threshold denied the party any realistic mechanism to address it.
Proposition 108 requires opt-out votes before October 1 in odd-numbered years. The earliest a successful vote could take effect is 2028.
If Republicans do opt out, their candidates would reach the general election ballot only through caucuses and assemblies. That system connects directly to a case HCA covered in February.
Rachel Suh filed Suh v. Griswold in January 2026, challenging Colorado’s delegation of binding ballot-access authority to private political parties through the precinct caucus system. Suh affirmed parties’ right to associate freely and conduct internal nomination processes. She argued that parties do not have a constitutional right to exercise delegated government power — binding authority over which candidates appear on public election ballots — while excluding 1.7 million unaffiliated voters.
Denver District Judge Andrew McCallin denied Suh’s preliminary injunction on February 5, applying the same Supreme Court precedent Brimmer relied on — California Democratic Party v. Jones. Brimmer used Jones to find the party has a right to exclude non-members from its nomination process. McCallin used Jones to find the party has a right to hold caucuses free from state interference. The two rulings point in opposite directions on the same constitutional question.
Suh raised a separate issue neither court addressed: whether Colorado has the authority under Article III of the state constitution to delegate ballot-access determinations to private parties. McCallin skipped that question and treated the case as an associational rights matter. Brimmer’s ruling did not reach it either. The delegation question remains unexamined by any Colorado court.
The Secretary of State’s office said it was “disappointed” and is evaluating an appeal with the Attorney General. Kent Thiry, the former DaVita CEO who financed Proposition 108, called the ruling “deeply flawed” and urged the state to appeal. The Colorado Republican Party did not respond to media requests.
The Brimmer ruling gives Republicans a lower threshold to close their primaries. If they use it, the nomination process defaults to the caucus system — a system whose constitutional foundation has been challenged but not tested on the grounds Suh raised.
Support Independent Local Journalism — High Country Advocate was created as a real alternative to regional media that too often silences dissenting voices while taking sides in the political struggle. Producing in-depth, unflinching reporting like this series and others is expensive: servers, editing, research time, and legal review all add up quickly. If these articles have informed you or given you new perspective, please consider supporting HCA with a paid subscription — every subscriber helps keep this reporting strong and independent. 