One challenge for Kennedy is that waiting for the perfect moment to depart can be dangerous. Past justices have made the wrong gamble. Thurgood Marshall, for example, was clear about his desire to retire while a liberal was president but, as his health failed, he was ultimately forced to give up his seat under George H.W. Bush. (He was then replaced by Clarence Thomas, who proved to be Marshall’s polar opposite.)

Ginsburg similarly refused to retire under Obama because she didn’t believe he’d be able to appoint a sufficiently liberal successor — and she is now grimly hanging on to her seat in her mid-80s to avoid departing under a Republican president she openly dislikes.

And even when a justice retires under seemingly ideal political circumstances, they still may not get an ideologically similar replacement. Sandra Day O’Connor — a Republican whose husband reportedly expressed horror at the prospect of an Al Gore presidency because she wanted to retire under a Republican — was ultimately able to step down under a fellow Republican, President George W. Bush. But she has subsequently criticized her replacement, Samuel Alito, for being too conservative.