A federal judge Thursday upheld Hawaii’s open primary election system, rejecting claims by the Democratic Party of Hawaii that allowing all voters to choose the party’s candidates is a violation of the First Amendment right to free association.

U.S. District Judge J. Michael Seabright ruled that the Democratic Party failed to prove that the open primary places a "severe burden" on the free-association rights of political parties, since some parties might embrace all voters. The judge also found that the party failed to present evidence that open primaries have allowed crossover or independent voters to select candidates that have changed the party’s message.

The Democratic Party sued the state Office of Elections in June, contending that the open primary system in place since 1980 was an unconstitutional violation of the First Amendment. The party argued that only voters who are Democrats or who publicly affiliate with the party before primaries should be allowed to participate to prevent anonymous voters who are indifferent or hostile to the party’s platform from choosing the party’s candidates.

The state attorney general’s office, which represented Scott Nago, the state’s chief election officer, defended the open primary as a system that protects voter privacy and encourages voter participation by removing barriers to voting.

"I think it’s a very sound ruling, and I’m very pleased with the result," said state Deputy Attorney General Deirdre Marie-Iha.

Tony Gill, an attorney representing the Democratic Party, said he wanted time to digest the court’s ruling before commenting on the substance. But Gill, former chairman of Oahu Democrats, said that the issue of associational rights is extremely important to the party.

"We think it will make a better society, and we think it will make a better party that way," he said of changing the open primary system. "So we’re not simply going to fold up and go away."

The party’s lawsuit accentuated a difference of opinion between party activists and many of the party’s most prominent elected officials, including Gov. Neil Abercrombie and state House and Senate leadership.

Some in the party’s rank and file are disappointed that elected Democrats, who have dominated politics in Hawaii since statehood, have not used their majority power to realize more of the party’s platform. The party has also welcomed several former Republicans who switched parties to have more influence in public policy.

Abercrombie and other elected Democrats have countered that the party’s "big tent" philosophy demands that all voters be able to participate in party primaries. The party has about 65,000 members, for example, but more than 237,000 voters participated in the Democratic primary in 2012.

Voters approved the open primary system through a 1978 constitutional amendment meant to protect voter privacy and encourage voter participation. Hawaii had a closed primary, where voters had to publicly declare party preference, from 1968 to 1978.

Hawaii Republicans had refused to join the Democratic Party’s legal challenge and welcomed all voters to participate in GOP primaries.

Judge Seabright, in his written ruling, said the Democratic Party’s "logic assumes too much," adding, "The right at issue is the right to associate, which includes the corollary right not to associate. And although the DPH may not want to associate with non-members, other parties may embrace association with anyone — party members or not — willing to vote in that party’s primary."

Seabright also noted that in California Democratic Party v. Jones, the U.S. Supreme Court’s ruling in 2000 that held that a blanket primary system, allowing multiparty votes, was an unconstitutional violation of the First Amendment right to free association, political parties had presented data and expert testimony on the impact of crossover and independent voters on the party’s message.

"In short, the DPH’s arguments rest on assumptions about voter behavior that cannot be judged without evidence," the judge wrote.