TO MEASURE the influence Dick Cheney wields within the White House, it is worth asking whether the United States would have gone to war in Iraq if he had not been Vice-President.

The latest book to convulse Washington, Bob Woodward’s 440-page account of the build-up to war, does not pose the question in so many words. But it goes a long way to answering it. It is the third book this year which shines a light into the shadows where Mr Cheney has spent the past three years, hiding from terrorists, avoiding the limelight, yet dominating the Administration.

In Plan of Attack, Mr Woodward’s book, some old acquaintances of Mr Cheney identify a sea change in the man over his handling of Iraq. Colin Powell, the Secretary of State, had regarded Mr Cheney as a “cool operator” when they had run the 1991 Gulf War, himself as Chairman of the Joint Chiefs of Staff and Mr Cheney as Defence Secretary. Now he saw Mr Cheney overtaken by “a kind of fever”.

“Powell saw in Cheney a sad transformation,” writes Mr Woodward. “He was not the steady, unemotional rock that he had witnessed a dozen years earlier. Cheney now had an unhealthy fixation. He was beyond hell-bent for action against Saddam. It was as if nothing else existed.”

The story of Dick Cheney and Iraq is illuminating both as a study of the most powerful Vice-President in US history, and of the inner workings of the Bush White House. General Powell is not the only one scratching his head. Some associates have spent decades alongside the unassuming man from Casper, Wyoming, and still do not know what makes him tick.

Listen to Paul O’Neill, the former Treasury Secretary hired by Mr Cheney at the start of the Bush II Administration. Mr O’Neill goes back with Mr Cheney to the Ford Administration in the mid-1970s, and expected him to be the same pragmatic voice and guardian of “sensible policy” that he remembered.

Yet Mr O’Neill found a different man when they took office in 2001, as he related in a book published after his 2002 sacking.

“He was never one to take a position and dig in, to be strident. Or so we all thought. We thought that we knew Dick. But did we? About this time people first started to ask, has Dick changed? Or did we just not know him before? Dick seemed to become ideological — and not so attentive to deliberation and evidence — and people started to wonder what happened.”

Mr O’Neill’s ignorance is no accident. Silence and secrecy are key elements in the Cheney act that have sustained him at the top of Washington into a fourth decade. Along the way he has been helped by rarely having to be the front man.

Under Nixon and Ford he played second fiddle to Donald Rumsfeld until succeeding him as Chief of Staff at the age of 34. As Defence Secretary to the first President Bush, he was dwarfed in stature by James Baker, the Bush family friend and Secretary of State.

Throughout, Mr Cheney’s style has changed little. Colleagues caught up in policy differences with him, such as General Powell, are driven to distraction by his maddening inscrutability.

Famously, he never shows his cards until he has to. In his present job, that often means to Mr Bush, alone.

The role adopted by Mr Cheney in the vice-presidency has added extra layers to his mystique. He is largely invisible, rarely makes policy speeches — when he does, he speaks in the flattest of monotones with head bowed, as if he were addressing his armpit — and last gave a press conference in 1991.

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