White House in denial as Rove is named as a possible 'leak' of CIA agent's identity

At a photo opportunity in the Oval Office, the President ignored a direct question yesterday whether he would sack Mr Rove, in keeping with his promise of June 2004 that he would dismiss anyone found to have been a leaker.

But the questions will not end there. The row over the disclosure of the name of a CIA covert operative, Valerie Plame, which has already led to one journalist being jailed for refusing to reveal her source, is turning into the most threatening scandal of Mr Bush's four and a half years in office.

Questioned by reporters for the second successive day, Scott McClellan, the White House spokesman, refused to discuss the Rove case. But on Capitol Hill, senior Democrats demanded that Mr Rove be dismissed, and called for congressional hearings into the affair.

"Karl Rove - the person at the centre of the slash-and-burn, smear-and-divide tactics that have come to characterise the Bush administration - has to go," John Kerry, the 2004 Democratic presidential candidate, wrote to supporters in an e-mail that summed up his party's long-held bitterness towards Mr Bush's adviser. Hillary Clinton, the New York senator (and a possible 2008 nominee for her party) also called on the President to fire Mr Rove.

The Plame affair has been simmering since her name was published two years ago by Robert Novak, a conservative columnist. The leak was widely assumed to be an act of revenge by the administration against Ms Plame's husband, the former ambassador Joseph Wilson, after Mr Wilson accused the Bush administration of grossly exaggerating pre-war intelligence over Iraq's weapons.

But it flared up at the weekend with disclosure of an internal e-mail at Time magazine, whose reporter, Matthew Cooper, was subpoenaed by the prosecutor probing whether the leak had been deliberate - a crime under US law.

Mr Cooper only avoided following the New York Times reporter Judith Miller to jail last week when Time agreed to hand over Mr Cooper's notes to the grand jury, and he said he would testify to the grand jury.

In the e-mail, obtained by Time's rival, Newsweek, Mr Cooper tells of a conversation he had with Mr Rove on 11 July 2003 - three days before Ms Plame's name was made public by Mr Novak. According to the e-mail, Mr Rove told Mr Cooper that Mr Wilson's wife worked for the CIA.

The revelation could hardly be more embarrassing for the White House.

Back in September and October 2003, Mr McClellan denied that Mr Rove had been involved with the leak. The suggestion was "ridiculous," he said then, adding "the President knows that Karl Rove was not involved." Those statements, in Watergate parlance, would now seem to be "inoperative".

For some two decades, Mr Rove has played a major part in Mr Bush's stunningly successful political career - as architect of his four victorious campaigns for Texas governor and the presidency, and currently as White House deputy chief of staff, involved in all areas of policy-making.

Now, to the delight of the Democrats, their nemesis is losing his lustre - and an administration that has so far been remarkably scandal-free is finally getting a taste of what life was like for the Clinton White House, beset by one special prosecutor's investigation after another.

There are, however, big differences. Unlike Republicans in the Clinton era, the Democrats control neither the Senate nor the House of Representatives, and cannot initiate hearings which could be especially damaging to the White House.

Moreover, legal experts say Mr Rove - so far at least - does not appear to have broken the law. A person has only committed a crime if he knows that the name disclosed was of a covert agent. The disclosure must be "intentional" and the leaker has to be aware that the CIA was taking steps to protect the operative's identity.

At the very least, however, the Rove affair will be a distraction to the White House and a further blow to its credibility.

And, just conceivably, Mr Wilson may yet be granted his wish, of seeing Mr Rove "frogmarched out of the White House in handcuffs".