Unaffiliated voters, who make up the largest share of Colorado’s electorate, will still be allowed to participate in the state’s Republican primaries after a federal judge Friday rejected the Colorado GOP’s latest attempt to exclude them.

Chief U.S. District Court Judge Philip A. Brimmer found the GOP failed to prove that Colorado’s law allowing unaffiliated voters to cast ballots in partisan primaries violates Republicans’ constitutional rights. He also wrote that the party “presented no evidence suggesting that Colorado’s semi-open primary system causes candidates to moderate or change their policy stances on specific issues.”

The decision may be appealed, though it’s not clear there’s enough time for an appeal to be settled before the primaries on June 25.

“Let us read the opinion first,” Colorado GOP Chairman Dave Williams texted Friday to The Colorado Sun.

Brimmer’s ruling comes after the Colorado GOP sought a preliminary injunction to unwind Proposition 108, the 2016 ballot measure that lets unaffiliated voters cast ballots in the state’s partisan primaries. The rejection of their request is the latest example of the party’s failed attempts at challenging the law, which was widely approved by voters.

During a two-day hearing in federal court last week, the party pleaded its case, arguing that Proposition 108 is unconstitutional because political parties are private organizations and nonparty members shouldn’t be allowed to help choose their general election candidates.

Attorneys for the party argued that allowing nonparty members to participate in their primaries dilutes the votes of party members in violation of their First Amendment rights of freedom to associate.

“It’s one of the most critical functions of a political party,” said attorney John Eastman, who is representing the Colorado GOP. “The right to associate includes the right of who not to associate with.”

Eastman was indicted over the summer alongside former President Donald Trump in Georgia for their efforts to overturn the results of the 2020 election. Eastman awaits a decision in California over an attempt to disbar him.

In the Colorado case, the party argued that the one mechanism they have to block Proposition 108 – persuading 75% of their central committee to withdraw from the primaries – is impossible to achieve. Only 34% of the GOP central committee voted to opt out in 2022, while 64% voted to opt out of the 2024 primaries at a Sept. 30 meeting.

Lawyers for the state defended the law and said that blocking unaffiliated voters from the June 25 primaries this year is unfeasible.

“We’re in the middle of a presidential primary election during which we cannot make changes,” said Hilary Rudy, deputy elections administrator at the Colorado Secretary of State’s Office. “I think we’d need six to nine months.”

While the state manages ever-changing voter registration data, Colorado’s primary elections are operated by clerks in 64 counties and funded by the state and county governments, not by the political parties.

Even if a change could be made, it would confuse unaffiliated voters who were allowed to participate in the presidential primary and wouldn’t be able to participate in the statewide primary election, Rudy said. About 48% of the state’s active voters are unaffiliated.

Several prominent Colorado Republicans testified in the case – for and against the GOP.

Former GOP Chairman Dick Wadhams and former Deputy Colorado Secretary of State Suzanne Taheri testified on behalf of the Secretary of State’s Office in support of allowing unaffiliated voters to participate in Republican primaries. Wadhams sparred with Randy Corporon, another attorney representing the Colorado GOP in the case, over Wadhams’ criticism of Williams.

Williams testified that allowing unaffiliated voters to participate in Republican primaries has resulted in weaker, less conservative candidates being advanced to general elections, particularly in 2022, when more unaffiliated voters participated in the GOP primary than in past years.

“I felt the open primary system that the Republican Party was forced into was detrimental,” he said. “Political parties have the right to nominate people who are best in line with their party platforms and the open primary system runs counter to that.”

But Brimmer wrote in his ruling Friday that “a political party does not have a constitutional right to nominate its candidates by a certain method.”

Brimmer also wrote that the party’s “inability to opt out of the semi-open primary for the last three election cycles is not due to an impossible structural barrier, but rather arises from robust policy disagreement within the party.”

The Colorado GOP filed the federal lawsuit in late July, before the central committee’s opt-out vote, but didn’t seek an injunction to prohibit unaffiliated voter participation until late December.

The rejection of the preliminary injunction Friday isn’t the end of the case. Republicans can still pursue the lawsuit, but it may take years to resolve.

A federal judge dismissed a similar lawsuit in 2022 brought by Republican activists.

Unaffiliated voters became the largest share of the state’s electorate in 2013, eclipsing the number of active, registered Democrats and Republicans in Colorado. Their numbers have only increased since Proposition 108 passed.

At the end of 2023, nearly 48% of active voters were unaffiliated, while about 27% registered as Democrats and 24% as Republicans.

The Colorado Sun is a reader-supported, nonpartisan news organization dedicated to covering Colorado issues. To learn more, go to coloradosun.com.