Median of Majority Coalition--Not Author--Drives Supreme Court Precedent

The Supreme Court's hidden power broker isn't the opinion author, but the median justice within the majority coalition. This conversation with Jonathan P. Kastellec reveals that traditional models of judicial decision-making, focusing on individual justices or the median of the entire court, miss a crucial dynamic: the strategic bargaining that occurs after a preliminary vote. The implication for legal scholars, political scientists, and anyone trying to understand the Court's trajectory is profound: understanding the coalition's internal negotiations is key to predicting the direction and durability of precedent. This nuanced view challenges the common perception of a monolithic Court, highlighting instead a complex interplay of individual preferences, institutional constraints, and strategic maneuvering that shapes the law in less obvious ways.

The Median of the Majority: Where Bargaining Power Truly Resides

The study of judicial politics has long grappled with how decisions are made on the Supreme Court. Early models focused on a purely legalistic approach, suggesting judges were bound by the letter of the law. This was challenged by the "attitudinal model," which posited that judges' decisions were driven by their personal policy preferences. A more sophisticated view, the "strategic model," recognized that justices operate within an institutional context, influenced by law, their own preferences, and the actions of other actors, including lower courts and the executive branch.

Jonathan P. Kastellec, in his work with Isaac Cape, delves into a critical aspect of this strategic model: the bargaining power within the Court. He argues that traditional theories, such as the "median voter theory" (where the median justice of the entire court is pivotal) or the "author theory" (where the justice assigned to write the opinion holds the most sway), fail to capture the full picture. Instead, Kastellec and Cape propose that the "median of the majority coalition" is the true locus of power.

This theory hinges on a fundamental difference between legislatures and courts. While legislatures vote on policy, courts decide disputes and then articulate rules via opinions. This process allows for concurrences and dissents, creating a complex bargaining environment. The core idea is that once a preliminary majority of justices agrees on a disposition (who wins the case), the opinion writer must craft a rule that satisfies the least content justice within that majority. This incentivizes the writer to cater to the median member of the winning coalition, rather than solely their own ideal point or the median of the entire court.

"The median of the majority theory... takes seriously the idea that courts do something that legislatures do not... Courts decide disputes... and what they do is something interesting they decide two things first who wins and who loses... but that's not mainly what the Supreme Court does the Supreme Court sets policy that all courts and other actors in the country are supposed to follow and to do that they write rules via opinions."

This dynamic has significant implications. If the median of the majority coalition is the driving force, then policy outcomes might be more extreme than predicted by the median of the entire court, especially in a ideologically divided Court. The bargaining power shifts from the individual author to the collective. The author's task is not just to express their own views, but to forge consensus within the winning bloc, a process that inherently pulls the opinion towards the center of that bloc.

The Erosion of Precedent: A Measure of Coalitional Power

To test these competing theories, Kastellec and his co-author collected extensive data on Supreme Court citations from 1953 to 2023. They analyzed how future cases (progeny cases) treated earlier decisions (origin precedents), categorizing these treatments as positive or negative. A negative treatment, such as distinguishing or overruling a precedent, signals a potential erosion of its authority.

The researchers then compared the predictive power of three different measures against the likelihood of negative treatment:
1. The author's ideal point: The ideological position of the justice who wrote the original opinion.
2. The median of the entire court: The ideological position of the median justice on the nine-member court at the time the progeny case was decided.
3. The median of the majority coalition: The ideological position of the median justice within the coalition that formed the majority in the progeny case.

The empirical findings, while nuanced, leaned heavily in favor of the "median of the majority coalition" theory. The distance between the median of the majority coalition and the origin precedent’s ideological position was a stronger predictor of negative treatment than the author's ideal point or even the median of the entire court.

"The probability that we get a negative treatment is better predicted right or the coefficient is stronger on the two median measures compared to the absolute measures."

This suggests that the ideological composition of the winning coalition in a subsequent case is more influential in determining how existing precedent is treated than who originally wrote the opinion or the overall ideological balance of the court at that future time. This implies that the internal dynamics and bargaining within the majority bloc are crucial. When a new majority forms, its internal median exerts a gravitational pull on how it interprets and applies existing law. If the new majority is ideologically distant from an older precedent, that precedent is more likely to be distinguished, modified, or overruled.

The research also highlighted that the author's influence, while present, was less predictive than the coalitional dynamics. This challenges the intuitive notion that the person writing the opinion holds the reins of power. Instead, the author is constrained by the need to maintain the support of the majority coalition.

The Uncomfortable Truth: Delaying Gratification for Durable Advantage

The findings from Kastellec's research offer a stark lesson for those seeking to understand or influence the Court: the most impactful decisions are often the result of patient, strategic bargaining within shifting coalitions, not the pronouncements of individual justices. This has direct implications for how legal strategies are formed and how the Court's future direction is assessed.

Here are some actionable takeaways:

• Focus on Coalition Dynamics: When analyzing Supreme Court decisions or anticipating future ones, look beyond the individual justices and consider the likely composition of the majority coalition. Understanding who is likely to be in the "median" position within that coalition is more critical than focusing solely on the Chief Justice or the most ideologically extreme justices.
  • Immediate Action: When reviewing past decisions, identify the specific justices who formed the majority and consider their relative ideological positions.
• Recognize the Power of "Negative Treatment": The gradual erosion or outright overruling of precedents is a key indicator of shifts in the Court's underlying dynamics. Pay attention to how often and in what ways older decisions are distinguished or challenged.
  • Over the next quarter: Track how recent Supreme Court decisions engage with or depart from foundational precedents in areas of interest.
• Understand the Median's Constraint: The opinion author is not free to write whatever they please. Their primary constraint is securing enough votes for a majority opinion. This means concessions to the median member of the coalition are inevitable.
  • This pays off in 12-18 months: When evaluating legal arguments, consider how they might appeal to a potential median justice within a likely majority coalition, rather than solely to the most ideologically extreme members.
• Anticipate Coalitional Shifts: The composition of the majority coalition can change from case to case. This means the "median" of the Court can effectively shift depending on the specific issue and the justices participating.
  • Immediate Action: When analyzing a specific legal question, consider which justices are most likely to form a majority based on their known issue positions.
• The Author is a Negotiator, Not a Dictator: While the author has influence, their power is largely derived from their ability to synthesize the views of the majority coalition. Their writing style and emphasis can matter, but only within the bounds of what the coalition will accept.
  • Over the next year: Recognize that legal strategies that appeal to a broad consensus within a likely bloc of justices may be more successful than those relying on the singular vision of a specific justice.
• Theory and Empirics Complement Each Other: While the empirical data provides strong support for the median of the majority theory, theoretical understanding of judicial incentives and bargaining remains crucial for interpreting these findings and for understanding the nuances that quantitative data might miss.
  • Long-term investment: Continuously engage with both theoretical scholarship on judicial behavior and empirical studies like Kastellec's to build a comprehensive understanding of the Court.