In the careers of all prime ministers there comes a turning point. He or she makes a fatal mistake from which there is no ultimate recovery.
OPINION: With Tony Blair it was the Iraq war and the failure to find weapons of mass destruction. With John Major it was Black Wednesday and sterling's eviction from the exchange rate mechanism. With Harold Wilson, the pound's devaluation in 1967 wrecked his reputation.
Each time the pattern is strikingly similar. Before, there is a new leader with dynamism, integrity and carrying the faith of the nation. Afterwards, the prime minister can stagger on for years, but as increasingly damaged goods: never is it glad, confident morning again.
David Cameron, who has returned from Afghanistan as a profoundly damaged figure, now faces exactly such a crisis. The series of disgusting revelations concerning his friends and associates from Rupert Murdoch's News International has permanently and irrevocably damaged his reputation.
Until now it has been easy to argue that Mr Cameron was properly grounded with a decent set of values. Unfortunately, it is impossible to make that assertion any longer. He has made not one, but a long succession of chronic personal misjudgments.
He should never have employed Andy Coulson, the News of the World editor, as his director of communications. He should never have cultivated Mr Murdoch. And - the worst mistake of all - he should never have allowed himself to become a close friend of Rebekah Brooks, the chief executive of News International, whose departure from that company in shame and disgrace can only be a matter of time.
We are talking about a pattern of behaviour here. Indeed, it might be better described as a course of action. Mr Cameron allowed himself to be drawn into a social coterie in which no respectable person, let alone a British prime minister, should be seen dead.
It was called the Chipping Norton set, an incestuous collection of louche, affluent, power-hungry and amoral Londoners, located in and around the prime minister's Oxfordshire constituency. Mrs Brooks and her husband, the former racing trainer Charlie Brooks, live less than two kilometres from David and Samantha Cameron's constituency home. The two couples meet frequently, and have continued to do so long after the phone hacking scandal became well known. PR fixer Matthew Freud, married to Murdoch's daughter Elisabeth, is another member of this Chipping Norton set.
When Mr Cameron bumped into Mr Freud at the wedding of Rebekah Brooks two years ago, he and Mr Freud greeted each other with exuberant high-fives to signal their exclusive friendship.
The prime minister cannot claim in defence that he was naively drawn into this lethal circle. He was warned - many times.
Shortly before the last election he was explicitly told about the company he was keeping. Alan Rusbridger - editor of The Guardian newspaper, which has performed such a wonderful service to public decency by bringing to light the shattering depravity of Mr Murdoch's newspaper empire - went to meet one of Mr Cameron's closest advisers shortly before the last election. He briefed this adviser carefully about Mr Coulson, telling him many troubling pieces of information that could not then be put into the public domain.
Rusbridger then went to see Nick Clegg, now the deputy prime minister. So Mr Cameron and Mr Clegg - the prime minister and the deputy prime minister - knew all about Mr Coulson before last May's coalition negotiations. And yet they both paid no attention and went on to make him the Downing Street director of communications, an indiscretion that beggars belief.
So the prime minister is in a mess. To put the matter rather more graphically, he is in a sewer. The question is this: how does he crawl out and salvage at least some of his reputation for decency and good judgment?
This is a potentially deadly moment. If Mr Cameron plays his cards wrong, his public image will change in a matter of a few days. From a popular and respected national leader, he will come to be defined by his ill-judged friendship with the Chipping Norton set.
This kind of personal degradation has happened before. By the end, Harold Wilson was irreparably damaged by his friendship with dodgy businessmen such as the raincoat manufacturer Lord Kagan. The Macmillan premiership fell apart under the weight of revelation from Lord Astor's Cliveden set.
So what must Mr Cameron do? First, he must speedily turn his back on Mrs Brooks. The Labour leader Ed Miliband was right on Wednesday to call on Mrs Brooks to consider her position at News International. At the moment, she is putting up the same defence as Mr Coulson when he was Mr Cameron's senior aide in Downing Street - that she did not know what was going on. Even if we accept this defence - and there is no strong reason to do so because News International has published many falsehoods in this sordid saga - it still does not work. Mrs Brooks, first as editor of the News of the World and The Sun and now as chief executive of News International, was responsible for setting standards. Those standards, as the world now knows, were foul beyond human credibility and she bears much of the blame.
It may well be dangerous for Mr Cameron to ditch Mrs Brooks. She may have acquired a great deal of information about him and the senior members of his cabinet, both at those quiet Chipping Norton dinners and quite possibly through other, nefarious means. Mrs Brooks is cornered and liable to strike out. But that is a risk the prime minister must take. Second, Mr Cameron must account for his actions. We need an explanation of how he came to hire Mr Coulson, what checks were made, what advice was taken. We need a checklist of those not so innocent social meetings with Mrs Brooks.
Hitherto, Downing Street has kept quiet about Mr Cameron's meetings with Mr Murdoch, thought to be one of the very first visitors he received after becoming prime minister. They now need to be made public.
It is essential this information be placed in the public domain because of the shocking decision made last week by the Coalition government to allow Mr Murdoch to entrench his monopoly power over the British media by buying the 61 per cent of the satellite broadcaster BSkyB he does not already own. This decision now stinks, and must be reversed.
On Wednesday, Mr Cameron muttered some vague phrases about the possibility of a public inquiry into phone-hacking - showing that he has not woken up to the fact that the world has changed utterly during the past 48 hours.
The horrifying revelations that Mr Murdoch's journalists hacked into the phone of the missing schoolgirl Milly Dowler and even into those of the families of our war dead have opened up a new level of horror about News International illegality.
The burning question now is whether US tycoon Murdoch - whose journalists have shown such open contempt for ordinary decency - is a fit and proper person to own any British publicly quoted company, and whether it is not time that his media organisation itself should be forcibly broken up.
Mr Cameron has allowed himself to be horribly compromised by his connection with News International and its employees. He urgently needs to regain the good sense and basic morality that have made him seem such an attractive prime minister. So he must use this terrible scandal, which has brought such shame on all journalists, as an opportunity to clean up British public life.
Judging by Wednesday, our greatly diminished prime minister shows no real appetite to do so.
- The Dominion Post
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