Supreme Court Justice Ruth Bader Ginsburg (Jonathan Ernst/Reuters)

With the estimable Brett Kavanaugh finally confirmed, conservatives now covet the Supreme Court seat held by 85-year-old Ruth Bader Ginsburg. The obvious thinking is that a 5-4 conservative majority is tenuous, but a 6-3 majority may ensure conservative dominance for decades. That’s quite true, but a different issue is whether a 6-3 Court would produce decisions that are more deeply conservative than a 5-4 Court would produce. On first impression, replacing a solid liberal such as Ginsburg with a solid conservative would surely shift decisions to the right. But not necessarily. It depends on who becomes the Court’s median voter.


I used to think the impact of a seat change is best measured by comparing the new justice to the old one, but that’s wrong. What we really want to know is what happens to the median (or swing) justice. The median justice provides the crucial fifth vote on cases that divide along ideological lines. So when Alito replaced O’Connor in 2005, the Court’s median justice switched from O’Connor to Kennedy. That was a slight rightward shift for the Court as a whole — but a smaller one than might be expected given Alito’s much more conservative record than O’Connor’s.

With Kavanaugh seated, the consensus is that Roberts will become the new median justice. This is a substantial movement to the right for the Court, especially on social issues where Kennedy typically voted with the liberals. Interestingly, in the short run it doesn’t matter where Kavanaugh fits in among the Court’s conservatives. Right now, Roberts is the least conservative, Thomas is the most, and Alito and Gorsuch fall in between. But whether Kavanaugh is closer to Roberts or to Thomas should have little effect on the Court’s rulings, since Roberts as the median justice will control the outcomes.


Where Kavanaugh’s ideology becomes important, however, is in determining the effect of replacing Ginsburg. If Kavanaugh turns out to be an Alito/Gorsuch–type justice, and so does Ginsburg’s replacement — let’s label that mystery person Amy B. — the median justice would be someone from the Alito-Gorsuch-Kavanaugh-Amy B. bloc. If you’re a conservative, shifting the median that far to the right would be a dream come true. It may cause a sea change in constitutional law.

But what if Kavanaugh turns out to be an ideological clone of Roberts? Then replacing Ginsburg with Amy B. would, in theory, have no effect on subsequent cases. The median justice would still have a Roberts-type ideology, and the Court’s decisions would continue to reflect his rightward but incrementalist approach.


Of course, this is a simplified model of how the Court behaves. Even in cases that divide justices ideologically, the groupings are not always predictable — e.g., Kennedy wanted to strike down Obamacare, but Roberts joined with the liberals to uphold it. A 6-3 Court is protected from that kind of surprise defection, while a 5-4 Court is not. There is also the intangible issue of how justices influence their colleagues behind closed doors. Nevertheless, the median justice exerts a lot of control over the Court, and we don’t know which justice will fill that role in the event that Ginsburg leaves.