The husband of a CIA agent who was outed during a row over Iraq has accused the White House of a "cover-up" involving top aide Karl Rove.
As top political strategist, Mr Rove is very close to Mr Bush
Political strategist Mr Rove has denied being behind the leaking of Valerie Plame's identity to the media in 2003.
It is alleged that Mr Rove spoke to a journalist about the agent, days before her name was revealed in the press.
Ms Plame's husband, former ambassador Joseph Wilson, added his voice to Democrat calls for Mr Rove to be fired.
"It's very clear to me that the ethical standard to which we should hold our senior public servants has been violated," he said at a press conference in Washington.
Mr Wilson has been a vocal critic of the Bush administration since July 2003, when he publicly challenged the government's arguments for going to war in Iraq.
PLAME AFFAIR TIMELINE
Feb 2002: Joseph Wilson looks into reports that Iraq tried to buy uranium in Niger
6 July 2003: Mr Wilson goes public about investigation
14 July 2003: Columnist Robert Novak writes the trip was inspired by Ms Plame - Matthew Cooper reports that he had similar information
30 September: Justice department launches probe
24 June 2004: President Bush testifies in case
15 July: Cooper and Judith Miller ordered to testify about sources
10 August: Miller and Cooper sentenced for contempt of court
28 June 2005: Supreme Court refuses to hear appeal
6 July: Miller jailed after appeals fail, Cooper agrees to testify
He says he travelled to Niger to investigate a claim that Iraq had tried to buy nuclear material there, but found no evidence to prove it.
The claim was later used by Mr Bush as part of the justification for the 2003 invasion.
It is alleged that senior administration officials leaked details of Ms Plame's role in a bid to undermine Mr Wilson.
He told NBC television "this thing... for the past two years has been a cover-up... of the... lies that underpin the justification for...war".
"And to a certain extent, this cover-up is becoming unravelled," he said.
"That's why you see the White House stonewalling."
This week, Newsweek magazine quoted Mr Rove's lawyer as saying his client did discuss Ms Plame with Time magazine journalist Matthew Cooper in an e-mail, but did not mention her name.
Democrats want the White House to reveal all the facts of the case.
President Bush has said he will withhold judgment about Mr Rove's involvement until a federal investigation into the leak is over.
Deliberate exposure of a covert agent is a criminal offence in the US.
Although Ms Plame's name was leaked in a different newspaper, Mr Cooper and fellow journalist Judith Miller of the New York Times were both ordered to testify about their sources in the case.
Mr Cooper later agreed after Mr Rove apparently said he could do so.
But Ms Miller maintained her refusal - arguing that it was her duty as a journalist to protect her sources - and was jailed.
The affair has led to a tense stand-off between the government and the media over the right of journalists to keep contacts confidential.