U.S. District Judge Lynn Winmill has declared Idaho's open primary election system unconstitutional with respect to the state's Republican Party primary, which the party passed a rule saying it wants to close. "An important corollary of the right to freely associate is a right not to associate," Winmill wrote in the decision, issued today. He found "clear evidence of crossover voting" in Idaho's primaries.

Though the states' expert testimony showed that closing the primary "will likely have the 'very real and immediate effect of . . . producing more ideologically extreme candidates,'” Winmill wrote, "At first blush, that would appear to be a strong argument for maintaining the status quo. But, choosing ideologically extreme candidates is precisely what a political party is entitled to do in asserting its right of association under the First Amendment." You can read the judge's decision here.