Decisions More Conservative Liberal 9-0 8-1 7-2 6-3 5-4 5-4 6-3 7-2 8-1 9-0

The Supreme Court under Chief Justice John G. Roberts Jr. has been a conservative court. But even conservative courts have liberal terms – and the term that ended Monday leaned left. The court issued liberal decisions in 56 percent of cases this term, according to the Supreme Court Database, using a widely accepted standard developed by political scientists. The final percentage is the highest since the era of the notably liberal court of the 1950s and 1960s led by Chief Justice Earl Warren. The closest contenders are the previous term and the one that started in 2004 and ended with the announcement of Justice Sandra Day O’Connor’s retirement. The term's two blockbusters, on same-sex marriage and health care, were both liberal, as were an array of discrimination cases. The trend was not uniform, and the court ended its term with conservative decisions in death penalty and environmental cases. The court's leftward movement is modest, and it remains well to the right of where it was in the Warren court years, when the percentage of liberal decisions routinely topped 70 percent. Yet the recent numbers do seem suggestive of a shift. The most conservative term since before the Warren court era was the fourth one of the court led by Chief Justice Roberts, in 2008, and the first term of the Roberts court was close behind. Conservatives certainly have many reasons to be happy with the Supreme Court’s recent work. On campaign finance, gun rights, race and abortion, the justices have delivered strongly conservative rulings. At the same time, the court does seem to have drifted slightly to the left since 2008, in part because of rulings on gay rights, health care and the environment. The chart above shows how the court has voted in every case by term — starting in October, usually ending the following June — since 1946. Decisions considered liberal are blue, and ones considered conservative are red, with darker shades representing more unanimity. The chart makes clear that the court moved left in the early 1950s, remained there for almost two decades and has generally leaned right for the past 40 years. It is obviously possible to quarrel with the coding of any individual case. But there is relatively little disagreement about the judgments among legal scholars, and the coding conventions are both consistently applied and in line with most people’s intuitions. Some examples: Decisions favoring criminal defendants, unions and people claiming discrimination or violation of their civil rights are considered liberal. Decisions striking down economic regulations and favoring prosecutors, employers and the government are conservative. Not all Supreme Court cases have the same significance, of course. Some matter much more than others. If the court had ruled on the conservative side on the blockbuster same-sex marriage case, the 2014-15 term may have not been remembered as a liberal one.

Closely Divided Decisions and Justice Anthony M. Kennedy

The crucial vote on the current Supreme Court usually belongs to Justice Anthony M. Kennedy. In 5-to-4 cases in the Roberts court era, he is usually in the majority, more often than not leaning right. But in the current term, he has gone left more often than right in 5-4 cases, including in a decision on congressional redistricting announced on Monday. The chart above shows the rise in Justice Kennedy’s power after Justice O’Connor left the court in the middle of the 2005 term. Before then, 5-4 decisions that leaned liberal frequently happened without him in the majority. Such cases have been less common in the last decade. But the current term has been a bit different in this way, as well. One of the other four Republican-appointed justices has joined the liberal side in about half of the 5-4 left-leaning decisions. Chief Justice Roberts has been the second most frequent justice to do so, with Justice Clarence Thomas also doing so on occasion. Justice Kennedy replaced Justice Lewis F. Powell Jr., who was similarly at the court’s ideological center. He too was more likely to vote in a conservative direction when the court was closely divided.

Overall Trends v. Major Cases

Indeed, a look at some of the Supreme Court’s biggest cases suggests that overall trends are only sometimes good indicators of individual results. Take Brown v. Board of Education, the landmark 1954 decision that said segregated public schools were unconstitutional. It was decided unanimously in Chief Justice Warren’s first term, when the court’s decisions were about equally divided between conservative and liberal ones. For the rest of the Warren court years, liberal decisions were far more common. In the term after Brown was decided, there were no unanimous conservative decisions. Brown was both a huge case in its own right and a harbinger of the court's direction. But by the time the Supreme Court identified a constitutional right to abortion in 1973 in Roe v. Wade, Chief Justice Warren E. Burger and three other appointees of Richard M. Nixon had started to move the court to the right. Roe was an exception to that trend, though it was not especially controversial when it was decided, as suggested by the 7-to-2 vote. In more recent years, general trends and the outcomes in big decisions have often aligned. In 2000, for instance, the court struck down a Nebraska law banning an abortion procedure by 5-to-4 in Stenberg v. Carhart, with Justice O’Connor in the majority. Over all that term, the court’s decisions were about evenly divided between liberal and conservative ones. Seven years later, after Justice O’Connor had been replaced by the more conservative Justice Samuel A. Alito Jr., the court upheld a similar federal law, the Partial-Birth Abortion Act, by the same 5-to-4 vote in Gonzales v. Carhart. By that point, in the early part of the Roberts court, 57 percent of the court’s decisions were conservative. Something similar happened in 2010 in Citizens United v. Federal Election Commission, a 5-to-4 decision that allowed corporations and unions to spend unlimited sums in candidate elections. That decision overruled part of a 2003 opinion from Justice O’Connor in McConnell v. Federal Election Commission, another 5-to-4 ruling. Here again, the arrival of Justice Alito appears to have changed the course of the law. Since 2010, the court's most consequential ruling was probably upholding Mr. Obama's health care law in 2012. That ruling leaned left, for the most part, much as the Roberts court has stopped leaning quite as far to the right as it did in its initial years.