U.S. Supreme Court justices on Thursday quizzed lawyers for Donald Trump and Special Counsel Jack Smith about the former president’s claim of immunity from prosecution for trying to undo his 2020 election loss, posing questions about what happens if a president sells nuclear secrets, takes a bribe or orders a coup or assassination.

Trump appealed after lower courts rejected his request to be shielded from four election-related criminal charges on the grounds that he was serving as president when he took the actions that led to the indictment obtained by Special Counsel Jack Smith.

Michael Dreeben, representing the special counsel, told the justices that the Supreme Court has never recognized the kind of immunity that Trump seeks for a public official.

Conservative Chief Justice John Roberts signaled concern about relying merely on the “good faith” of the prosecutors to prevent abusive prosecutions against presidents if the Supreme Court rejects presidential immunity.

“Now you know,” Roberts told Dreeben, “how easy it is in many cases for a prosecutor to get a grand jury to bring an indictment. And reliance on the good faith of the prosecutor may not be enough in some cases - I’m not suggesting here” in Smith’s indictment of Trump.