Here’s how our proposal would work. Each president would get to appoint one (or perhaps two, more on that in a minute) justice at some point in their first term. The beginning of the second year seems like a logical moment; it would be after they have had a stab at their principal legislative agenda and before any midterm referendums. If they get reelected, they would get to appoint another justice (or two) in their second term.

When vacancies arise by death or retirement, they would not (directly) be filled. The court might, therefore, have 10, 11, 12 or 13 justices, or it might have seven, eight, or nine. What this scenario would not have is the opportunity for one president to get to make more nominations than another, nor the opportunity for a justice to time their retirement to maximize the chances of an ideologically compatible successor, nor the opportunity for the Senate to hold open a vacancy until the next election to place such an explicit partisan referendum on the court.

For the justices, it would free them to retire when they want to, or to choose not to retire at all, allowing them to serve for as long as they feel they are contributing to the court. If the justices themselves feel strongly that a particular size of the court is appropriate, they would be free to establish norms — formal or informal — about retirement age, with senior justices retiring when the court reaches a certain size or retiring in pairs across the ideological spectrum.