Has a political week ever been so shaped by pictures? The appalling photos of the abuse visited upon Iraqi prisoners by grinning men and women serving in the "world's finest military" have devastated America's image around the world, brought a mighty defence secretary to the brink of resignation, and sent tremors through a once thriving presidency.
But as George Bush feels these cold and unaccustomed chills of political mortality, it may not be those shocking images that will cause him most concern. Rather it is a number - or more accurately a variety of numbers - published in various polls this week, measuring his approval rating.
They show that this crucial measure has fallen for the first time to 50 per cent or below. Not since Harry Truman in his miraculous come-back year of 1948 has a president won a second term from such a slender base of popularity at this point in the election cycle.
Mr Bush's goose of course is not yet cooked. "Events, dear boy, events," Harold Macmillan famously remarked when asked what was the trickiest and most unpredictable part of government. The remark applies to this president as to few others.
Conceivably, the situation will improve, or at least calm down sufficiently to give the White House a breathing space. With Iraqi security forces on its streets, Fallujah may quieten down. The Shia religious establishment in the south may bring the fiery anti-American cleric Muqtada Sadr to heel.
The United Nations special envoy Lakhdar Brahimi may yet conjure up a formula that averts disaster at the limited handover of sovereignty that Mr Bush insists will still take place in less than eight weeks.
Alternatively, the disorder may worsen, as the appalling pictures from Abu Ghraib empty the already dwindling reservoir of support for the US. More foreign insurgents may flock to the cause, US military casualties could rise - and this week's poll figures for Mr Bush might soon start looking a fond and distant memory.
Taken together, the violence in Fallujah, the administrative shambles on the ground and Abu Ghraib, may become the Iraq occupation's equivalent of the Tet offensive in Vietnam in 1968 - the moment when public opinion tips decisively against the war.
Americans still believe - just - that Mr Bush was right to invade Iraq. But if a majority shifts to believing that the war was a mistake, then a president who has made the invasion the centrepiece of his war against terror may be doomed to defeat.
Then there is the damage inflicted on Mr Bush's own image. The myth of the decisive commander-in-chief running a tight and perfectly harmonious ship has been destroyed.
The fissures have been on display for all - as well as the unique spectacle of this White House letting it be known that Mr Bush had given Donald Rumsfeld a dressing down, and the latest show of dissent from Colin Powell (through, as usual, his proxies) in an astonishingly blunt magazine article.
Republican strategists have drawn comfort from the failure of John Kerry to turn the worst week of the Bush presidency to his advantage. In fact the Massachusetts Senator has played his hand well. When the week began, with the first anniversary of Mr Bush's "Mission Accomplished" fiasco, he avoided the temptation to gloat.
He has not issued a strident call for Mr Rumsfeld to resign - pointing out that he has been making that demand for six months, once it had become evident that the postwar occupation has been utterly botched. In the past few days, Mr Kerry has improved his position (which, incidently, is already far better than that of Bill Clinton at the same point of the 1992 campaign).
In short, the message of the polls is probably bleaker for Mr Bush than for his opponent. But just possibly, an entirely different number will be the salvation of Mr Bush this autumn.
According to Department of Labour yesterday, the rebounding economy created 288,000 new jobs in April, the second bumper month on the employment front.
If the trend continues, by November Americans may be concluding that prosperity at home is more important than ignominy abroad. If so, Mr Bush may get his second term.
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