Unanimity in the Supreme Court used to be the norm. In the early Supreme Court there were few dissents and so there was little opportunity to see differences between the justices’ views outside of how they authored their majority opinions. This practice has changed over the years as now decisions are more frequently divided rather than unanimous.

Certain justices are also more and less likely to vote alongside one another. Differences in voting agreements can be somewhat staggering. Last term, for instance, Justice Thomas voted at least in part along with Justices Roberts, Gorsuch, Alito, and Kavanaugh at least 75% of the time each. By contrast he voted along with Justices Ginsburg and Sotomayor 50% of the time each, Justice Breyer 51% of the time, and Justice Kagan 60% of the time. Justice Sotomayor voted at least in part with Justices Kagan, Breyer, and Ginsburg at least 85% of the time. Along with her 50% agreement with Justice Thomas, she voted with Justice Roberts 67% of the time, Justice Alito 57% of the time, Justice Gorsuch 63% of the time and Justice Kavanaugh 64% of the time.  

These agreement levels are based on unanimous as well as divided votes. Thus, the majority of the time justices like Thomas and Sotomayor vote together, other justices vote alongside them as well. Seldom do we see justices that vote with each other less frequently, vote together in isolation.  Justices Thomas and Sotomayor only once voted together in dissent without any other justices in the 2015 Term case Voisine v. United States.

Over time the justices’ voting agreements are captured together in certain ideology measures. Martin Quinn (MQ) Scores for instance are based on justices’ voting agreements as justices with closer scores vote together more frequently and distance between justices’ scores increases as they vote together less frequently. Positive MQ Scores equate with a more conservative ideology and negative scores equate with a more liberal ideology. Ideology in this instance, however, is merely a function of voting alignment. The Justices MQ Scores for the 1994 through 2018 terms are shown in the graph below.

This period is important because it begins with Justice Breyer’s first year on the Court. After Justice Breyer joined the Court, the Court’s membership was stable until Justice Rehnquist passed away in 2005.  Similar to the data in the agreement tables, the justices’ MQ Scores tend to cluster into three groups. The more liberal justices have more negative numbers and include Justices Breyer, Souter, Stevens, Kagan, Ginsburg, and Sotomayor. The more conservative justices have more positive numbers and include Justices Thomas, Scalia, Alito, Gorsuch, Renquist, Roberts, and Kavanaugh. Justices Kennedy and O’Connor, although both moderately conservative, were the most moderate justices during this period falling towards the middle of the graph.  

One implication of the graph and voting agreements is that we do not often expect to see a single more conservative justices vote along with only a liberal justice or several liberal justices and we do not often expect to see a more liberal justice vote along with a conservative justice or several conservative justices.  Such decisions are referred to as “cross-ideological” for the purpose of this post.  As support for the proposition that this does not occur very often we have only seen it twice so far in argued cases decided so far this term: in Thryv, Inc. v. Click-To-Call Technologies, LP Justices Sotomayor and Gorsuch dissented together and in Ramos v. Louisiana Justice Kagan dissented alongside Justices Alito and Roberts.  This is the first time ever that we have seen either of these dissenting coalitions and interestingly enough, both of these decisions they were released on the same day, April 20^th, 2020.

As these cross-ideological coalitions do not arise very frequently, they lead to interesting questions such as when and why they occur.  Justice Kagan’s vote in Ramos was explained as being predicated on different reasons than Justices Roberts and Alito’s.  According to this argument Justices Roberts and Alito’s votes in this case regarding the unanimity of jury verdicts was in favor of the more conservative approach which while Justice Kagan’s vote was in favor of upholding precedent (which was overturned in this decision). Justice Kagan’s adherence to precedent is seen as especially important based on her powerful dissent in Knick v. Township of Scott last term where she emphatically questioned the basis for the majority overturning its past decision in Williamson County Regional Planning Comm’n v. Hamilton Bank of Johnson City.  

Pooling all of the cases with such cross-ideological votes since the 1994 term we see a few trends of interest.  First of all is an uptick in such votes in liberal decisions according to data from the United States Supreme Court Database which has conservative or liberal decision codings for most of the Court’s decisions. This increase can be discerned from the following graphs which show the fraction of liberal decisions with cross-ideological votes on top (both the percentage of votes and the count of votes) and the percentage of liberal decisions in all cases below. The gray lines show the trends over time.

Liberal decisions have been trending upwards as a percentage of total decisions moving from about 40% of the decisions in 1994 to closer to 50% of the total decisions in 2018. This includes all unanimous as well as divided decisions. Cross-ideological decisions have moved at about double the pace in the liberal direction from also around 40% of the total cross-ideological decisions to around 60% of the cross-ideological decisions in 2018.

Justices may be strategically moderating their positions on specific issues to reach cross-ideological consensus and since the liberal justices on the Court are outnumbered by their more conservative counterparts, the liberal justices are possibly more strategic about moderating their positions to bring in a conservative justice to create a majority or when they dissent to join ideologically distant colleagues on the Court.

When we break down the cross-ideological decisions by issue we see differences between the most common case types with cross-ideological votes and the most common case types in all cases that the Court heard between OT 1994 and 2018. The cross-ideological graph is on top and the all-decisions graph is below.

Habeas corpus cases dominate the Court’s main docket dwarfing other issues in comparison. They play a much more minute role in the cross-ideological decisions. Search and seize and criminal sentencing cases are on top of the cross-ideological cases. Both are important issues in the Court’s main docket although several issues are more dominant than criminal sentencing including natural resources and First Amendment cases.

Another important area for cross-ideological decisions is judicial review of administrative agency cases. This issue is also within the Top 20 issues on the Court’s main docket although it falls much lower in the list.

State and federal tax cases are both high on the cross-ideological case list and although federal taxation makes it onto the Court’s main docket list, state taxation does not.  Other areas on the cross-ideological case issue list that are on the Court’s main issue list include:

• right to counsel,
• punitive damages,
• state jurisdiction over Indian law cases,
• double jeopardy, due process,
• and miscellaneous criminal law cases.

Case areas on the Court’s most common issue list that are not on the cross-ideological list include:

• natural resources,
• government and civil rights liability,
• ERISA,
• Deportation,
• Campaign finance,
• and Supreme Court docket fees for indigent petitioners

One further difference we see between the Court’s overall merits docket and cross-ideological decisions is with the majority decision authors. Opinion authorship for the Court’s merits docket is generally spread evenly among the justices.  This is not so for cross-ideological decisions. Cross-ideological decisions obviously raise issues that divide the justices in interesting ways. This in turn leads to majority author assignment to justices who are able to speak for the fractured majorities in these divided decisions. The figures below look at the percentage of majority opinions the justices authored to normalize the numbers between cross-ideological and all decisions for comparison purposes. The cross-ideological decision authors are on top with the graph with all decision authors below.

In both graphs, the justices that spent the most time on the Court during this period tended to write the greatest fractions of opinions. Still, there are notable differences. Kennedy authored over 3.5% more cross-ideological opinions than all opinions even though he was on top of both charts. As Kennedy is often seen as the swing justice for much of this period, it is little surprise that he had an exaggerated role speaking for fractured majorities.

Breyer authored 2.5% more of cross-ideological opinions than all opinions though he also was the second most frequent author on both charts. The biggest apparent difference is with Justice Scalia. Scalia authored over 11% of all authored opinions from OT 1994 through OT 2018, yet he only authored 6.44% of cross-ideological majority opinions. Whether this had to do with the issues in the decisions or with his position in the dissents versus the majorities, his frequency of authoring cross-ideological opinions was quite low relative to his overall majority authorship frequency.

There are a few other differences of note. Like Justice Scalia, Justice Souter authored a greater percentage of overall majority opinions relative to cross-ideological opinions, but his difference was a more moderate approximately 2.5%. Looking lower down the chart, Roberts and Sotomayor both authored greater frequencies of cross-ideological opinions while Alito, and O’Connor both authored greater shares of overall opinions rather than cross-ideological ones.

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The analysis above began by showing that there are clear differences in the justices’ voting patterns and that the justices tend to vote with some justices much more frequently than with others. It went on to show that the cases where justices vote with ideologically distant justices have particular contours. They tend towards certain issues. They also lead to certain differences in majority authorship. This analysis both informs our understanding of what brings unique justice coalitions together and begs further questions that are heretofore unanswerable. Since we know little about what goes on behind the scenes in the Supreme Court we don’t know what bargaining brings these justices together. Perhaps multiple drafts of opinions were authored to bring about certain consensus. Perhaps the justices’ are not as ideologically constrained as some of the numbers suggest. In any case, these unique combinations of justices showcase the justices’ abilities to reach consensus in a time when differences of opinions are more often the subject of discussion.

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On Twitter: @AdamSFeldman