If Prop 1 passes, the measure would make two big changes to the state’s elections. Instead of the closed Republican primary (and separate, but open, Democratic primary), all voters would participate in a single “blanket” primary.

Idaho voters roundly rejected Proposition 1 on Election Day, stopping a measure that would have transformed the state’s elections. Unofficial results showed that only 30.4% of residents voted yes — and more than two-thirds voted no. The tally ...