The end of the Supreme Court term looms, and with it the prospect — the terrifying prospect — of a retirement. Specifically, the retirement of Justice Anthony M. Kennedy, who will turn 81 next month and is the longest-serving current justice, named to the high court almost 30 years ago.

So if Kennedy is inclined to retire, it is hard to begrudge him that choice. But his departure would be terrible for the court and terrible for the country. It could not come at a worse time. Any court vacancy these days, under a president of either party, triggers a battle between liberal and conservative forces. Kennedy’s retirement would unleash nomination Armageddon, given the feral political environment and the pivotal role he plays on the closely divided court.

To understand the impact of Kennedy’s departure, just look back to his selection to fill the seat vacated by Justice Lewis Powell. Like Kennedy now, Powell was the ultimate swing justice; his was the key fifth vote for liberals on issues including abortion rights and affirmative action, topics as charged then as they are today.