US Vice-President Dick Cheney will not testify in defence of his former top aide, who is accused of lying to federal investigators, lawyers say.
There seems to be no precedent for a vice-president testifying
The ex-aide, Lewis "Scooter" Libby, will also not take the stand in his own defence, his lawyers have announced.
Mr Libby is accused of trying to block an investigation into who revealed that the wife of a prominent White House critic worked for the CIA.
Historians say no vice-president has ever testified at a criminal trial.
The prospect that Mr Cheney might take the stand in defence of Mr Libby had prompted great excitement.
But Mr Libby's lawyer, Theodore Wells, said on Tuesday he would not call the vice-president - after suggesting in December that he would.
Mr Wells also said Mr Libby would not take the stand - prompting Judge Reggie Walton to ask Mr Libby to rise and confirm he was giving up the right to defend himself.
A number of high-profile Washington journalists testified in Mr Libby's defence on Monday, and his successor as Mr Cheney's chief of staff took the stand on Tuesday.
The prosecution spent three weeks arguing that Mr Libby had revealed the identity of the CIA agent, Valerie Plame, well before he admitted to having known it.
It is a crime knowingly to disclose the identity of an undercover agent.
No-one was ever charged with the leak, but Mr Libby was charged with five counts of perjury and obstruction for comments he made to investigators.
His defence argues that any incorrect statements he may have made were the result of a faulty memory, not an attempt to deceive.
His successor in Mr Cheney's office, John Hannah, testified on Tuesday that Mr Libby did indeed have a bad memory.