Geoffrey Wheatcroft: A shiny new face, but yet to win over either his party or the nation

On the whole the British are suspicious of "charismatic" politicians, and it's unusual for someone to explode on to the scene with one brilliant rhetorical performance in the way Barack Obama did when his electrifying speech at the 2004 Democratic convention led to the White House.

Recently we've seen two exceptions: Nick Clegg changing the rules of the game with his appearance in the first televised debate last month, and before that, David Cameron seizing the Tory leadership with his bravura speech at the 2005 party conference. Or were they such exceptions? Clegg-mania was for a moment so acute that the Liberal Democrats began to hope that they could overtake Labour in the popular vote, but it might always have been Cole Porter's "toy balloon that's fated soon to pop". So it proved on Thursday – when another balloon was punctured as well.

An election which was disappointing for all the parties was bitterest of all for the Tories. Whereas it would have been beyond the Lib Dems' wildest dreams to win more than 100 seats, the Tories had every reason a few months ago to think they would win the election with a parliamentary majority, rather than a plurality which leaves them bargaining and horse-trading.

What went wrong? Might the answer just possibly be the man who is succeeding Gordon Brown as prime minister? Could it be that the British electorate, not to put too fine a point on it, saw through Dave? In some ways he is a type perfectly familiar to those who recall the Tory party within living memory, when Sir Alec Douglas-Home's Cabinet in 1963 contained 11 Old Etonians. But nowadays Cameron's background seems exotic, the handsome country home in Berkshire, the aristocratic connections, the prosperous stockbroker father who was chairman of White's, grandest of London clubs: altogether the most gleaming of silver spoons.

This is a little unfair. Though scarcely a meritocrat, Cameron is no brainless booby. After Eton he went to Oxford where, as the world knows, he was a member of the Bullingdon Club, who dress up in fancy blue tailcoats, get drunk, and behave foolishly. But he also took a First in Politics, Philosophy and Economics, and the constitutional historian Vernon Bogdanor says that he was one of the ablest pupils he ever taught.

Once upon a time such a man would have got an honest job, at the Bar, in the army, in business, or even journalism. But like too many others nowadays, Cameron went straight "into politics" – by joining the Conservative Research Department and working as a special adviser. It was not a happy choice, since by September 1992 he found himself advising Norman Lamont, the Chancellor. On that indelible evening of Black Wednesday, when sterling was forced out of the exchange rate mechanism, the camera caught young Dave lurking behind Lamont as he made his humiliating statement, a photograph which, unlike the Bullingdon portrait, he has been unable to suppress.

Then it was seven years in the nearest thing to a proper profession he ever came, as "director of corporate affairs" at Carlton Communications. But maybe not quite so proper. There was something misplaced as well as vulgar in the Labour attacks on Cameron as a "toff". They got the wrong "on": it should have been not Eton or Bullingdon but Carlton. What that job title meant was that he was the PR spin doctor at a television company full of sharp elbows, and he did not enhance his own reputation while there. Jeff Randall of The Daily Telegraph and Sky, sometime Business Editor of the BBC, is a bluff sort of bloke, and patently honest with it. When he said, after his dealings with Cameron at Carlton, "I wouldn't trust him with my daughter's pocket money... In my experience, he never gave a straight answer when dissemblance was a plausible alternative", it might be a warning.

Having married his pretty, rich wife Samantha, Cameron started looking for a parliamentary constituency. She works for Smythsons, the elegant and expensive Blond Street stationers, where her income is no doubt a useful supplement. The Camerons have a young son and a daughter. Their eldest son was gravely handicapped, and died aged six last year, after several harrowing years for the family, an ordeal which was endured with dignity and won much sympathy. She is now pregnant again, the baby due in September.

After standing unsuccessfully at the 1997 election, Cameron tried but failed more than once to find another constituency before being chosen for Witney in Oxfordshire. Cameron was elected to parliament in 2001, and became party leader little more than five years later.

Few politicians are entirely consistent and Cameron shouldn't be judged too harshly for every single about-turn. Still, the way he became leader brought wintry smiles to the lips of some MPs and political correspondents. First he worked closely with Michael Howard, the last party leader, and helped draft the bare-knuckle rightist manifesto at the 2005 election. Then he was the beneficiary of Howard's cunning strategy after that election, delaying his own departure so as to shaft David Davis and bring forward Cameron.

He then made a very good start as Tory leader, even if his new caring and compassionate incarnation was a little soon after that manifesto. And yet at some stage the shine has worn off. There has been something desperate about the attempt to reinvent Cameron as an ordinary chap, and as green as they come. No one has forgotten the ludicrous stunt when he cycled to Westminster from his home in Notting Hill, followed as it turned out by a large car bearing his clean shirts.

Since then there has been one bewildering volte-face after another, now hugging hoodies, now tough on crime, now promising to favour the family through taxation, now changing his mind. To begin with he tried to present himself as "Blair's heir", perhaps egged on by Michael Gove, one of his closest front-bench associates and the man who once wrote, "I can't fight my feelings any more: I love Tony." Perhaps Cameron finally worked out that, whatever Gove may think, most ordinary Tories – and other citizens – had come to detest and despise Blair.

And Cameron's sheer lack of judgement has been alarming. Only the week before last he flew to Belfast to strike a deal with the Ulster Unionists, a crazy mission. Worse still – the worst single moment in his party leadership – was the summer before last, when Cameron flew to Tiflis during the conflict between Georgia and Russia, and said that Georgia should be admitted to Nato immediately. Apart from the fact that, as plenty of us guessed at the time and has since been confirmed by independent observers, Georgia was not in the right, Cameron's words meant, if he was serious, that he was ready to send the Coldstream Guards to fight and die for South Ossetia. Did he mean it?

Now Cameron enters No 10 without a clear mandate from the public and with a number of powerful and barely quiescent enemies in his ranks. In the strange new landscape we have entered, anything might happen – even the final disintegration of the Tories, the oldest political party in Europe.

Geoffrey Wheatcroft's books include 'The Strange Death of Tory England' and 'Yo, Blair!'