Currently political parties set the rules for selection of candidates to run in the primary elections. A small number of people can thus select the candidates the voters get to vote on.
“I don’t care who does the electing, so long as I get to do the nominating.”
Boss Tweed
An alternative approach would be to eliminate political party primaries. Registered voters would vote on all the candidates that meet the initial requirements and choose the final two candidates who will compete in a run-off election. Ranked choice voting could be used to select from a potentially large number of primary candidates to ensure that run-off candidates have substantial support.