U.S. Supreme Court justices generally are reluctant to step aside from cases and leave their colleagues in potential deadlocks. But Chief Justice John Roberts Jr. may have little choice if President Donald Trump heads to court to restrict current or former administration officials from testifying at his impeachment trial.

Trump has suggested he may seek to assert executive privilege to protect the office of the presidency if his former national security adviser, John Bolton, is called on to testify at the ongoing Senate impeachment trial. The possibility of such a move has spurred considerable attention in recent days, as legal scholars weigh the novelty of an executive privilege claim arising in the context of impeachment.