A major political row has broken out in Washington following allegations that officials in the Bush administration leaked the name of a CIA agent to take revenge on a critic of its decision to go to war with Iraq. The Justice Department has launched a criminal inquiry.
The officer named, Valerie Plame, is the wife of a former US ambassador, Joseph Wilson, who challenged a claim that Iraq had tried to buy uranium in Africa.
BBC News Online world affairs correspondent Paul Reynolds looks at the issues.
How did this all start?
It started in February 2002 when Joseph C Wilson IV, a retired career diplomat and former American ambassador to the west African state of Gabon, was asked by the CIA to go to Niger, also in west Africa, and investigate reports that Iraq had tried to buy uranium there.
Such an attempt would indicate a plan by Iraq to build a nuclear bomb since it had no civilian nuclear programme.
Mr Wilson came back and reported that he did not believe the reports.
Nevertheless, President Bush referred to them in his State of the Union address in January this year.
He pinned the information on the British Government which still stands by it.
The CIA later admitted that allowing such a reference in the speech was a mistake since, unlike the British Government, it did not regard the intelligence as reliable.
Then on 6 July this year, Mr Wilson went public about his mission in the New York Times. He added this criticism: "I have little choice but to conclude that some of the intelligence related to Iraq's nuclear weapons programme was twisted to exaggerate the Iraqi threat".
How did the White House respond?
Veteran Washington columnist Robert Novak, whose report prompted this row, said that he was "interviewing a senior administration official on Ambassador Wilson's report when he told me the trip was inspired by his wife, a CIA employee working on weapons of mass destruction. Another senior official told me the same thing".
Mr Novak reported this in his syndicated column on 14 July. It did not cause much of a stir at the time.
He has since added that the official who spoke to him was "no partisan gunslinger" and that it had been an "offhand revelation." He had called another official for confirmation and this official said: "Oh, you know about it."
The Washington Post has reported that "two top government officials called at least six Washington journalists and disclosed the identity and occupation of Wilson's wife, Valerie Plame".
However Novak says the "report that someone in the White House failed to plant this story with six reporters and finally found me as a willing pawn is simply not true."
Why reporters other than Novak did not make more of the information is a mystery.
Why would the White House want to undermine Joseph Wilson?
The implication is that the White House was trying to suggest Wilson had a hidden motive for his trip to Niger. He once worked on the National Security Council for President Clinton and was seen by the Bush White House as an opponent.
Novak says Wilson had become a critic of the President's policy in Iraq and had contributed to the Al Gore campaign in the last election and to Senator John Kerry in this.
It is not known exactly what Valerie Plame's role in the CIA is or was. Novak says he was told she was an analyst, but the fact that the CIA is taking legal action suggests she did have an undercover role. As a former diplomat's wife, she would have travelled widely.
Why has it taken so long for this row to develop?
The story became a major one only when it emerged that the CIA had asked the Justice Department to open an inquiry into the leak.
It is a crime for an official to reveal the name of a CIA undercover operative to someone without security clearance and the CIA always follows up such leaks. The penalty upon conviction is up to 10 years in prison. The reporter who receives such information is protected.
News of the CIA request propelled the story from the level of political gossip to the level of political crisis.
Reporters who might have sat on the story or who did not follow it up have been criticised but there has also been a debate about whether the naming of a CIA employee in this way was a proper exercise of journalistic freedom.
Who might have leaked the name?
This is the big question in Washington right now.
The White House has denied that it was Karl Rove, who is the president's closest domestic political adviser.
The White House spokesman, Scott McClellan, said that Rove and two other officials, Lewis Libby the vice president's chief of staff and Elliott Abrams of the National Security Council, had told him they were not involved: "They were not involved in leaking classified information nor did they condone it."
McClellan said that if any officials were found to have leaked the name, they would be sacked.
Joseph Wilson has been quoted as saying: "It's of keen interest to me to see whether or not we can get Karl Rove frog-marched out of the White House in handcuffs. And trust me, when I use that name, I measure my words."
Mr Bush told his staff: "I want to get to the bottom of this."
Robert Novak himself refuses to disclose his sources.
Do the Democrats smell blood?
Yes. The Democrats think that not only can they flush out the source, thereby potentially causing damage to the administration, but that all this concentrates attention on the weaknesses in the case presented by President Bush for going to war.
Already senior figures from both parties on the House of Representatives Intelligence Committee have questioned the basis of the intelligence used to justify the war.
What kind of inquiry is being carried out?
The Justice Department has announced that it has scaled up its preliminary investigation into a full-scale criminal probe. White House staff have been told to cooperate and to preserve documents.
The Democrats have demanded an independent inquiry, not one led by the Justice Department, which is headed by a close ally of Mr Bush, the Attorney General, John Ashcroft.
The Justice Department has not ruled out bringing in an independent figure at a later stage (former Senator George Mitchell has been mentioned) but for the moment the inquiry is in the hands of professional lawyers and FBI agents.
Whether the investigation will reveal the source is by no means certain. Traditionally, leakers are notoriously difficult to identify given the secrecy involved and the fact that the reporters are unlikely to name their contacts.