The White House says President Bush has confidence in senior aide Karl Rove who is at the centre of a scandal over the leaking of a CIA officer's identity.
Karl Rove is one of President Bush's closest advisers
Democrats called for a full account of the revelations that Mr Rove spoke to a journalist about the agent days before her identity was revealed in the press.
The White House has previously refused to comment on the affair, citing an ongoing criminal investigation.
A trusted Bush adviser, Mr Rove has denied being behind the 2003 leaking.
This week, Newsweek magazine quoted Mr Rove's lawyer, Robert Luskin, as saying his client did discuss Ms Plame with Time magazine journalist Matthew Cooper in an email but did not mention her name.
Democrats called on the White House to reveal all the facts of the case.
"If these allegations are true this rises above politics and is about our national security," said Senate Minority leader Harry Reid.
He said he hoped President Bush would follow through on a pledge to sack anyone involved in leaking the agent's name.
The president himself did not respond to a question about Mr Rove at a press briefing on Tuesday.
But White House spokesman Scott McClellan confirmed Mr Bush still had faith in Mr Rove, breaking his silence after two days of pointed questioning on the affair.
"Any individual who works here at the White House has the president's confidence," Mr McClellan told reporters.
"They wouldn't be working here if they didn't have the president's confidence."
But he refused to discuss the matter in detail.
"I don't want to do anything to jeopardise the investigation. And just because I'm not commenting on a continuing investigation that doesn't mean you should read anything into it beyond that."
Prosecutors are investigating how the identity of Ms Plame was revealed in the media in 2003.
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.
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
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.
Correspondents say that, while it is up to prosecutors to find out whether a crime has been committed, the government's credibility is now at stake because of previous denials by Mr Rove.
Ms Plame's husband, former US ambassador Joseph Wilson, has alleged that his wife's identity was made public in an attempt to discredit him after he challenged the government's arguments for going to war in Iraq.
Mr Wilson said he travelled to Niger to investigate a claim that Iraq had tried to buy nuclear material there but found no evidence to prove it.
Mr Luskin said Mr Rove's e-mail to Mr Cooper said that Ms Plame had authorised the trip.
Its purpose was to discourage Time magazine from publishing false allegations that Vice-President Dick Cheney was behind the trip, not to deliberately expose Ms Plame, he added.
The Niger claim was used by President Bush as one of the reasons for invading Iraq.