Ranked-choice voting -- which already exists for state primary, congressional and presidential elections in Maine and a number of large cities in local elections -- is a small tweak to existing voting rules. Under current plurality voting, your ballot offers a list of candidates, but you can only choose one. Most people choose a Democrat or a Republican, because these are the only two parties most people believe have a shot of winning, and so anything else is just a wasted vote, or worse, a spoiler vote that winds up helping the candidate you absolutely don't want.