Denver Post:

Opening Colorado’s primary elections to unaffiliated voters has cost partisans their constitutional right to free association, a group of Republicans are alleging in a new lawsuit.

The lawsuit, filed Feb. 24 in federal court by four current or former candidates for office and a GOP party chair, seeks to let parties close their nominating elections again to just party members, and with hopes to do so in time for the June primaries.

One of the lawyers who filed the lawsuit is John Eastman, the former visiting scholar at the University of Colorado Boulder who advised then-President Donald Trump on how to overturn the 2020 election.

“The First Amendment to the United States Constitution includes the right of political parties to choose their nominees for office without interference by those who are not members of the party and have chosen not to affiliate with the party,” the lawsuit states….

In 2016, Colorado voters opened non-presidential primaries to unaffiliated voters 53% to 47%. A twin measure that returned Colorado to presidential primaries and opened them to unaffiliated voters passed by an even wider measure, 64% to 36%.

In the fall, Republican Party leaders roundly rejected invoking an opt-out clause of the 2016 referendum that would have returned the party’s nomination process to in-person caucuses and assemblies.