Justice Kennedy's departure from the Supreme Court will mark the end of the Early Roberts Court, or what many of us would often refer to as the "Kennedy Court." Justice Kennedy was in the Court's majority more often than any other justice. His distinct jurisprudence, combined with his position as the Court's median justice, meant that his particular (and often idiosyncratic) views had a disproportionate impact on the Court's jurisprudence. What comes next will be interesting, and likely somewhat surprising.
Justice Kennedy is often described as a "moderate" justice, but this characterization does not quite capture what was distinct about Justice Kennedy's approach to the law. On most issues, most of the time, Justice Kennedy was a moderate conservative. He voted on the "conservative" side of most cases. When the Court split 5-4 along ideological lines, for instance, Justice Kennedy would side with the conservatives approximately two-thirds of the time. (64% since OT 2005.) Justice Kennedy had a narrow view of the protections afforded criminal defendants under the Bill of Rights, embraced federalism, generally (though not always) favored textualist approaches to statutory interpretation, supported a Chicago-School approach to antitrust, believed in gun rights, and was skeptical of class actions and entrepreneurial plaintiffs' litigation.
Although conservative, Justice Kennedy also usually preferred minimalist decisions of the sort favored by the Chief Justice over broad rulings setting forth categorical rules. When the Court split along Formalist-Pragmatist lines -- typically in criminal justice cases -- Justice Kennedy would also tend to side with the Pragmatists, eschewing bright-line rules in favor of more flexible assessments based on the specific exigencies of a given situation. In sum, the mode of Justice Kennedy's decision-making was a moderate conservative pragmatism.
While Justice Kennedy was usually a moderate conservative, there were areas of the law in which Justice Kennedy was not particularly moderate and others in which he was not particularly conservative. Particularly in areas touching on the freedom of speech and personal liberty, Justice Kennedy would swing for the fences. Justice Kennedy was easily the most speech-protective Justice on what was a quite speech-protective Court. Whether the speech at issue concerned political campaigns or product pricing, "offensive" messages or dishonest claims about military service, Justice Kennedy believed in uncompromising First Amendment protection. By some accounts it was Justice Kennedy who pushed the Court (and a reluctant Chief Justice) to invalidate the McCain-Feingold campaign finance law, and this would be entirely consistent with what we saw in his First Amendment opinions.
Speech was not the only freedom that mattered to Justice Kennedy. He had a deep concern for Due Process, as shown in his embrace of habeas rights for alleged enemy combatants, his concerns about the application of capital punishment to some classes of criminal defendants, and his embrace of constitutional limits on punitive damages. He also, perhaps most famously, believed that due regard for individual liberty barred the government from adopting laws prohibiting or disregarding same-sex relationships, as in Lawrence, Romer, Windsor, and Obergefell. In these areas, there was nothing modest, moderate, or minimalist about Justice Kennedy's views or the doctrinal rules he would embrace.
Given the makeup of the Roberts Court, as went Justice Kennedy, so went the Court. Where Kennedy was a moderate conservative favoring a minimalist approach, the Roberts court would tend to adopt a moderate conservative opinion. Where Justice Kennedy favored a more muscular approach, on the other hand, there were almost always at least four votes to go along. (NFIB v. Sebelius being a notable exception.) If Justice Kennedy wanted to recognize same-sex marriage or preclude the use of the death penalty for those convicted of non-lethal crimes, the liberals would agree. If Justice Kennedy wanted to protect campaign-related or commercial speech, the conservatives were there. so the Roberts Court was generally as conservative and as moderate as Justice Kennedy wanted to be.
Without Justice Kennedy on the Court, the particular (and sometimes peculiar) contours of the Roberts Court's jurisprudence are likely to change. In some areas, this is likely to move the Court in more conservative direction, but there are many areas in which the differences between Justice Kennedy and his replacement may be hard to predict, including (but not limited too) the First Amendment, the Dormant Commerce Clause, punitive damages, preemption, and criminal procedure. How the next justice feels about some of these questions could be quite significant (consider, for example, dormant commerce challenges to state climate rules or First Amendment challenges to mandatory disclosure requirements). These sorts of questions do not always divide jurists along right-left lines, so it's hard to predict how they will fall out.
One change we can predict is that Chief Justice Roberts will more often than not, be the new median justice, largely because of his minimalist approach to judging. Chief Justice Roberts, more than any other justice on the Court, believes in narrow rulings that attract broad majorities, answering no more than necessary to resolve a given case. The Chief Justice has been somewhat successful in pushing this approach over the past decade, but usually only when Justice Kennedy would go along (and the two of them agreed). Without Justice Kennedy, the Chief Justice may have a greater ability to steer the Court in a minimalist direction, even where his conservative colleagues disagree. In this regard, the Chief's decision for the Court in Bond v. United States, in which he joined with the liberals to adopt a narrower (yet still "conservative") outcome may be a sign of things to come.
One other change we can expect will be in the mix of cases the Court accepts for certiorari. In recent years, it has appeared that many justices based cert decisions (at least in part) on what they expected from Justice Kennedy. That will no longer be part of the calculus. Also, as scholars such as Thomas Merrill have noted, as the Court's personnel changes, it becomes more difficult (at least at first) for justices to predict case outcomes and thus it becomes more difficult to engage in strategic voting in the cert process. So don't be surprised if we start seeing a different mix of issues start to come before the Court.
To conclude this already overlong post, we can say with some certainty that the Kennedy Court is gone. It is more difficult to predict what the new Roberts Court will look like. To paraphrase the Swam, that's why they hear the cases.