Measuring a Judicial Legacy
One way to think about a career such as Justice Kennedy’s is to look at the opinions that he wrote or the cases where he probably supplied the decisive vote. You can also consider his extra-judicial acts or (years from now) assess his internal influence at the Court through memos.
Here’s another way of thinking about this though. Years from now, will anyone say something like “As Justice Kennedy reasoned” or “As Justice Kennedy explained” in an opinion or a brief? We see that with federal judges like Henry Friendly and Supreme Court Justices like Robert Jackson. And we have already seen that with Justice Scalia since his death. I doubt very much, though, that anyone will think invoking Justice Kennedy by name will convince anybody of anything in future.