Two states, California and Washington, have gone further, instituting “top two” primaries for non-presidential elections. All candidates compete in a single preliminary election, from which the two most popular proceed to the general, even if they’re both Democrats, Republicans, or neither.
The group Fair Vote argues persuasively that the egalitarian goals of top-two would be realized more consistently by a top-four primary followed by a ranked-choice general election. The latter, employed by several U.S. cities and other countries, has voters rank candidates by preference – first choice, second choice, etc. This enables an instant runoff: The voters’ first choices are tallied, the last-place candidate is eliminated, and the loser’s voters are allocated to the remaining candidates based on their second preferences. The process repeats until a candidate wins an outright majority.