What must a US Supreme Court justice do in order to stay on the bench?

All they have to do is avoid being declared crazy. They are appointed for life, so the only ground for impeachment is if they are incapable of continuing their job. I guess they also have to not resign...

Addition:

Supreme Court justices are not appointed for "life," but "during good behavior." They need to avoid committing "high crimes and misdemeanors," the constitutional phrase for impeachable offenses. Supreme Court justices may be impeached, convicted and removed from office for the same reasons the US President can be impeached.

* Justices who don't commit impeachable offenses may remain on the Court indefinitely, which is similar to a lifetime appointment.

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