Special prosecutor Patrick Fitzgerald is expected this week to wrap up a two-year investigation into the naming of the agent, Valerie Plame.

What began as little more than a parlour game question — who sent her husband Joseph Wilson, a former ambassador, to Niger to investigate dubious claims about the sale of uranium to Saddam Hussein’s Iraq? — has become a critical test of the integrity of the White House.

The omens are not good for Rove, the arch political operator known as “Bush’s brain”, and “Scooter” Libby, chief of staff to Dick Cheney, the vice-president. Despite earlier denials, evidence has accumulated that they suggested to reporters that Wilson’s mission was little more than a freebie for a critic of the administration, set up by his CIA wife.

At the time the CIA was at loggerheads with Cheney and his “Iraq group” of advisers over the strength of evidence for Saddam’s weapons of mass destruction programme. Wilson’s debunking of the uranium sales was seen as a hostile act.

There were signs this weekend that the president is distancing himself from the man he calls the architect of his election victories. If indicted, Rove and Libby are expected to step down immediately from their posts.

The stakes could not be higher, with Bush already reeling from attacks over the handling of Hurricane Katrina and the nomination of Harriet Miers, his personal lawyer, to the Supreme Court.

According to a presidential adviser, Bush carpeted Rove two years ago for his inept handling of the Plame controversy. “He made his displeasure known to Karl,” the adviser said. “He made his life miserable about this.”

Andrew Card, Bush’s chief of staff, last week emphasised the need for “honesty and ethics” at the White House. “Our job is to help the president do his job and it’s not to worry about each other,” Card said pointedly. He went on to list the “outstanding people” who advise the president, without mentioning Rove.

Card’s confidence in the depth of the Bush team is not shared by conservatives who fear that the president has already been suffering from Rove’s absence. When New Orleans was flooded, Rove was in hospital with kidney stones, and he has been tied up with “Plamegate” — being quizzed for four hours in his fourth appearance before a grand jury — while the Miers nomination has spun out of control.

“When you are in the gun sights of a special prosecutor, it is distracting,” said Bill Kristol of the neoconservative Weekly Standard magazine.

Speculation is growing that Miers may withdraw her Supreme Court nomination on the pretext that she is unable fully to answer senators’ hostile queries about her lack of a legal paper trail because so much of it concerns confidential White House advice.

“Ironically the person in the White House most qualified to play Rove’s role is Scooter Libby,” said one leading conservative analyst. “To lose either is a huge blow; to lose both is a catastrophe.”

Plamegate may come down to the question of whether Rove or Libby knowingly revealed the identity of a spy, a criminal offence, or whether a cover-up is the crime and they perjured themselves before a grand jury.

Or, indeed, whether the two aides merely defended their bosses from Wilson’s biased attack and did what everyone in Washington does — leak.

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