When he steps into court 73 at the Royal Courts of Justice at 10.30 this morning, Tony Blair knows that his future as Prime Minister could hinge on the next couple of hours.
His lines have been well-rehearsed during and since his family holiday at the Barbados villa of Sir Cliff Richard, which was eclipsed by the long shadow of the Hutton inquiry. Even if Lord Hutton does not cast a permanent shadow of blame over the Prime Minister in his report, his inquiry has already shone an unwelcome searchlight into the murky corners of the Blair regime.
Whatever Mr Blair's involvement in the events leading to the death of a government scientist, the process has dangerously eroded the public's trust in the Prime Minister. The implications for his political future go well beyond Lord Hutton's verdict. Close allies of Mr Blair are confident that the former barrister will comfortably survive his unexpected day in court. "He will emerge as clean as a whistle," one optimist said. Aides recalled that, on previous "big games", Mr Blair had "played a blinder".
Arguably, Mr Blair has had plenty of training. At his monthly press conferences, journalists have barely laid a glove on him. His decision to appear before a Commons select committee has not troubled him either. Mr Blair is the original master of not answering the question. The press are not allowed follow-ups, allowing him to move on quickly. But today may well be tougher. Perhaps he will meet his match in James Dingemans QC, counsel to the inquiry, who will be able to ask as many questions as he wants.
For Mr Blair, the stakes could hardly be higher. Today's appearance has been inevitable since the moment on 18 July when he was told on his Boeing 777 over the Pacific that David Kelly had disappeared from his Oxfordshire home. The triumph of Mr Blair's address to both Houses of Congress was over; tragedy was confirmed a few hours later. The smiling Prime Minister who boarded the plane in Washington was shaken and grey by the time he disembarked in Toyko.
Four days later, on a flight from Shanghai to Hong Kong, Mr Blair uttered the words he may live to regret to a scrum of journalists. Asked whether he had authorised the leaking of Dr Kelly's name, he replied: "Emphatically not. I did not authorise the leaking of the name of David Kelly."
The e-mails, memos and letters emerging at the inquiry now suggest otherwise. One telling note by Sir David Omand, the security and intelligence co-ordinator, is headed: "Meetings in the Prime Minister's study, 7 and 8 July 2003." These took the fateful decisions that Dr Kelly would appear before the Foreign Affairs Committee and to issue a statement that an official had come forward to say he had met the BBC journalist Andrew Gilligan.
Downing Street's strategy of saying that the Ministry of Defence was the "lead department" has been undermined by the weight of evidence submitted to the inquiry. It suffered further damage yesterday, when Geoff Hoon, the Defence Secretary, proved reluctant to take on the role of fall guy and sacrificial lamb.
Blair aides now wish they had called a truce in the battle with the BBC. Of course they would never have pursued it if they could have foreseen the consequences. But there was one man who could have called off the attack dogs. It wasn't Alastair Campbell, the chief rottweiler. It was Mr Blair.