President Biden has announced plans to create a bipartisan commission to study reforms to the Supreme Court. Among the options the commission will be studying are term limits for Supreme Court justices. The most prominent term limit proposals would replace the current system in which judges are appointed for life with a system in which they would be appointed for 18-year terms. Their tenures would be staggered so that two appointments would be made each presidential term.

Term limits appear popular with the public. Their appeal also cuts across partisan lines, and both liberals and conservatives have endorsed them. But what would the practical consequences be?

Our new academic article, Designing Supreme Court Term Limits, examines how term limits might play out in practice. We find that any of the major proposals would probably dramatically change the partisan balance of the Supreme Court, making lopsided majorities less likely. Differences in the details of the different proposals could also lead to major differences in the court’s decisions.

We simulated what would have happened in the past

Article III of the Constitution provides that judges serve “during good behavior,” which has been interpreted to mean that Supreme Court justices serve for life. Term limits proposals would change that by permitting justices to serve for only a limited period — 18 years under most proposals. Some proposals look to introduce a constitutional amendment while others impose limits through new laws, which is controversial, because many believe that life tenure is constitutionally required.

We studied how five different term limit proposals would have shaped the court if they had been in place during the last 80 years. One proposal imposed term limits on currently serving justices; the others all permit sitting justices to retain life tenure. One would begin immediately (so that there would be more than nine justices during a transition period), but another would wait until all sitting justices had left the Supreme Court.

We then ran mathematical simulations to see how each proposal would have shaped the court had it been in place over 50-year periods, starting in 1937, 1938, 1939 and so on. We used data on the historical life expectancy of federal judges to simulate justices’ unexpected deaths, allowing us to get a sense of the consequences of each plan had it been in place during recent American history. That allowed us to compare the likely consequences of each proposal against the existing system of life tenure.

Term limits would have led to less partisan and more closely divided courts

Our key finding was that all the major term limits proposals would have reduced the levels of extreme partisan imbalance over the last 80 years. It would have done this by preventing justices from strategically retiring at times when they could maintain their party’s advantage on the court. If we define extreme partisan imbalance as a situation in which seven or more of the nine justices have been appointed either by a Democratic or a Republican president, then the court has had such an imbalance 60 percent of the time over the last 80 years. Term limits would have cut this in half.

We just look at the membership of the court, but obviously the membership has important implications for how judges decide cases; the scholarship finds a strong relationship between partisanship and how justices vote.

For example, an extreme partisan imbalance on the court favored conservatives from 1972 until 2009, and our findings suggest that during this period the court would have been much more likely to be divided merely 5-4 on partisan lines under term limits. Because many important Supreme Court cases were decided 5-4 with conservative justices joining the liberals in dissent during this period, these cases could have come out differently had the court included composed of justices with different political leanings.

Reducing imbalances would mean a more closely divided court — that is, a court more often divided 5-4 along partisan lines (although, to be sure, justices do not invariably vote as their party of appointment might predict). And that could make it harder to get the Senate to confirm nominees when different parties hold the presidency and the Senate.

Potential pitfalls

Our simulations suggest that over half of new justices would join a court with a 4-4 partisan split, thus raising the partisan stakes — because the new member could potentially flip the court on key issues. That happened during the battle to replace Justice Antonin Scalia, the most recent vacancy with the potential to change the court’s ideological balance. In that case, the Republican Senate declined to hold a hearing for Judge Merrick Garland, President Barack Obama’s nominee. Those drawing up proposals might wish to consider rules for what might occur if the Senate refused to vote on a president’s nominee.

Our simulations also reveal big differences in how long the various proposals would need to take effect. The proposals that would begin appointing term-limited justices immediately could be fully implemented — with all nine active justices serving 18-year terms — in under 20 years. In contrast, proposals that delay the transition until current justices leave the court could take over 50 years, on average, to go fully into effect.

Introducing term limits is hard

Our analysis highlights the consequences of the different proposals for term limits, but they don’t make the political challenges any easier. Any term limit proposal would face difficult political and legal hurdles before it could actually become law. Statutory proposals face serious constitutional objections. The constitutional amendment proposals, by contrast, effectively require bipartisan consensus, as constitutional amendments have to be ratified by a supermajority of states.

It’s hard to see how Republicans and Democrats could agree. Republicans would likely object to imposing term limits on sitting justices, given their present supermajority. Democrats would be disadvantaged if term limits only apply to new appointments going forward.

Running simulations like ours can help to illustrate the consequences of different proposals, and hence inform public conversation.

Adam Chilton (@adamschilton) is a professor of law at the University of Chicago Law School.

Daniel Epps (@danepps) is an associate professor at Washington University School of Law.

Kyle Rozema (@kylerozema) is an associate professor at Washington University School of Law.

Maya Sen (@maya_sen) is a professor of public policy at Harvard University’s John F. Kennedy School of Government.