On January 25, U.S. District Court Judge Philip Brimmer, a Bush Jr. appointee, heard oral arguments in Colorado Republican Party v Griswold, 1:23cv-1948.  The law requires all parties that have primaries to allow independent voters to vote in those primaries, unless the State Central Committee by a vote of 75% of the members authorizes the party to close the primary.  Although a majority of the Republican Committee members want a closed primary, supporters of closing the primary have never been able to surmount the 75% threshold.

See this story about the argument.