Speculation over a possible vacancy has focused in recent years on the prospect of Justice Clarence Thomas exiting while Republicans control the White House and Senate, and alternatively on the health of the court's aging liberal bloc.

Top Senate Republicans drew fresh attention to the bench recently when they said they would confirm a new justice if given the chance despite 2020 being an election year, in an apparent reversal of their rationale for blocking President Obama's nominee late in his second term.

Such statements, including by Sen. Lindsey Graham (R-S.C.) earlier this month, revived the unsubstantiated whisper campaign that Thomas was considering retiring now to allow Republicans to replace him with a like-minded, though younger, jurist to lock down conservatives' 5-4 majority.