Justice Anthony Kennedy’s retirement announcement was not unexpected but is still major news in the direction and leadership of the country.

Kennedy spent more than 30 years on the Court and for much of that time, particularly the last decade, has been the deciding or “swing” vote on so many controversies, ranging from campaign finance to gay marriage, the Second Amendment to abortion. Throughout that time, his judicial philosophy couldn’t be pigeonholed as “conservative” or “liberal,” and indeed is hard to describe in conventional terms. Most terms he agreed with Cato’s position more than any other justice and so he’s also sometimes known as the Court’s “libertarian” justice. There’s some truth to that, even though he often reached results that libertarians liked for reasons that sounded in dignity and civility rather than classical-liberal or natural-rights theory.

Kennedy was the strongest defender of the First Amendment that the Court has probably ever seen, whether in the context of political or artistic expression made by students, workers, or any citizens. He was also a careful guarantor of the Constitution’s structural protections for liberty. Whether federalism, the separation of powers, or any of the other “less sexy” parts of constitutional design, he recognized that they were there as a means to protect and secure our liberties, not as a dry technical exercise.

By retiring now, Kennedy hands President Trump a golden opportunity to put his stamp on the Court. All of the people on the White House list of 25 potentials could be considered more reliably conservative than he has been—which means that Chief Justice John Roberts will become the median justice. Given that the Democrats pushed the Republicans to eliminate the filibuster, any Trump nominee should be able to be confirmed without too much fuss (assuming the most moderate GOP senators approve). That will have a significant impact on all the sorts of cases where Kennedy joined the more liberal justices to form a 5-4 majority—of which there were actually none this term.

In short, it was a momentous term that was made all the more momentous by this announcement.