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Column: Why the Supreme Court Will Always Split 5-4

Everyone knows that under Chief Justice John Roberts the U.S. Supreme Court often divides 5-4 — an even split between liberals and conservatives, with Justice Anthony Kennedy providing the swing vote. But here’s a puzzle. Over recent decades, and under many different chief justices, the share of 5-4 splits in the court’s docket has been fairly constant — on average, in the vicinity of 20 percent.

Is the court always split between liberals and conservatives, or is there some other explanation?

Before trying to answer this, we need to look at the data. Since 1981, there have been four years that stand out for an unusually high rate of 5-4 splits: In 1986, 1989, 2000 and 2006, around 30 percent of court decisions were divided that way. Four other years in the same period show an unusually low rate: In 1984, 1987, 1991 and 2005, less than 15 percent of decisions were 5-4 splits.

But those are the outlier years, and given the relatively small number of cases, it would be a mistake to make much of them. In the other 23 years, 5-4 splits fell in the narrow range between more than 15 percent and 25 percent or less. Over the past three decades, there has been no substantial trend toward either fewer or more 5-4 splits — or even any sustained period during which the percentage of 5-4 splits was unusually high or low.

Extend the time frame back to 1946, and you see broadly similar patterns. From 1946 to 1980, 5-4 splits often ranged from 15 percent to 25 percent.

A potential explanation for this relative consistency over more than six decades is that both Democratic and Republican presidents appoint justices, and unless one party dominates the presidency for a sustained period, the court will be pretty evenly divided between Democratic and Republican appointees. Since 2009, for instance, the court has included five justices appointed by Republican presidents (Samuel Alito, Anthony Kennedy, John Roberts, Clarence Thomas and Antonin Scalia) and four appointed by Democrats (Stephen Breyer, Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor).

The problem with this explanation is that for most of the past three decades, the court has been dominated by Republican appointees. In 1981, the court had just two Democratic appointees (Thurgood Marshall and Byron White) and seven Republican ones (Harry Blackmun, William Brennan, Warren Burger, Sandra Day O’Connor, Lewis Powell, William Rehnquist and John Paul Stevens). In 2001, a similar 7-2 split favored Republican appointees. In other words, the percentage of 5-4 splits has not significantly declined when presidents of one party have been able to select most of the court’s members.

Which bring us to another explanation: The court has been evenly divided on ideological grounds in part because Republican presidents have, intentionally or not, made some liberal or moderate choices. There is no question that Brennan (an Eisenhower appointee) and Blackmun (a Nixon appointee) showed quite liberal voting patterns. And many Republicans were disappointed by Stevens (a Ford appointee) and David Souter (named by George H.W. Bush). Maybe the persistent 5-4 divisions reflect persistent ideological divisions.

There is something to this explanation, but it is not adequate. To see why, imagine that over the next decade the only two justices to retire are the liberals Breyer and Ginsburg, and that they are replaced by people who tend to agree with Scalia and Thomas. In that event, the court would have six conservatives, and its center of gravity would shift sharply to the right. Would we see a reduction in 5-4 decisions? Don’t be sure, because lawyers and lower court judges are alert to the court’s composition. If it became dominated by conservatives, we would see a very different set of rulings from the lower courts, whose judges are not inclined to make a lot of decisions that are likely to be reversed.

The point is that the cases that the court hears will always consist, in large part, of issues that are difficult not in the abstract but in light of the court’s particular composition. In the modern era, a significant number of 5-4 decisions is likely — at least if the justices are not working hard to suppress internal dissent (as they did before the 1940s), and if lower courts are not systematically ignoring the court’s thinking.

It follows that any Supreme Court will probably seem “evenly divided” in a significant number of important cases. In a hierarchical legal system, the court will end up hearing disputes that are likely to split its current members — even if their ideology changes radically over time.

Cass R. Sunstein, the former administrator of the White House Office of Information and Regulatory Affairs, is a professor at Harvard Law School.Bloomberg View columnist.