Joan Smith: Sarkozy struts in Napoleon's clothes

France's taste for the flamboyant is being severely tested as the President shows off his trophy girlfriend Carla Bruni

Napoleon went to Egypt with 34,000 troops in search of glory. Nicolas Sarkozy went with Carla Bruni, for much the same reason. While most people who are newly in love dream of whisking the object of their affections to a luxury hotel, the President of the Republic chose to take his supermodel girlfriend on a tour of world-famous burial sites. Over Christmas it was Luxor and the Valley of the Kings, where the rulers of Egypt had themselves interred with maximum pomp; last weekend he whisked her to Jordan where another ancient civilisation, the Nabateans, built rock tombs in the rose-red city of Petra.

With his love, death and glory tour satisfactorily concluded, Sarkozy arrived back in Paris last week in bullish mood, apparently unaware of the imminent publication of no fewer than three books about his ex-wife, Cécilia. During a press conference at the Elysée Palace on Tuesday, Sarkozy couldn't resist showing off about his relationship with Bruni and had the nerve to claim that he was striking a blow against traditional French hypocrisy about politicians' private lives.

Journalists reeled under a sarcastic onslaught from their President, who harangued them for criticising his very public romance, while also reporting it in minute detail. No one thought to mention a parallel with Diana, Princess of Wales, who posed in front of another photogenic tomb, the Taj Mahal, when she wanted to send a signal to the media. Her message was that her husband was treating her badly; Sarkozy's signal was just as clear.

It was also a lot cruder. A satirical caption over the President's head as he steered Bruni towards Petra would have needed to consist of a mere three words: "I've pulled, me." It may be that the temporary discomfort of much of the French press last week was caused by guilt over journalists' silence in the face of previous presidents' infidelities. But Sarkozy was gambling with his luck and it quickly failed him when extracts from Anna Bitton's book Cécilia appeared in news magazines on Thursday.

The former first lady took legal action to prevent publication, claiming that the book was an invasion of her privacy. Her lawyers spent Friday in court, where she lost her case and immediately appealed against the decision. But the damage was already done and the whole of France, along with millions of awed observers in other countries, has been talking about Cécilia's scornful dismissal of her ex-husband. According to Bitton, a journalist and old friend of the second Mme Sarkozy, Cécilia has described her former husband as a sauteur or serial womaniser, accused him of being mean with money and claimed that he was incapable of love, even towards his sons. She described his lifestyle since their divorce in October as undignified, claiming that he plunged into a round of "karaoke parties until four in the morning".

Cécilia's words cannot be dismissed as those of a woman scorned. Most commentators agree that the Sarkozy marriage was over a couple of years ago – at Cécilia's instigation – and it's widely believed that she agreed to return to his side only to avoid damaging his chances of becoming President. Staying together for the sake of the elections suggests a residual affection towards Sarkozy on Cécilia's part and the possibility that she has only recently lost patience with her ex-husband.

According to Bitton's book, Cécilia believes that Sarkozy has "a ridiculous side". "He is undignified. Nicolas doesn't come over like a president. He has a real behaviour problem ... He needs someone to point it out to him. I did it for 18 years and I can't do it any more."

Whether Carla Bruni is prepared to step into the breach is unclear – new lovers are not renowned for taking a cold, hard look at each other – but the most damaging aspect of Cécilia's remarks is her suggestion that Sarkozy's behaviour lacks dignity. In France, unlike the UK, the president is also the head of state. Difficult though it is to imagine Tony Blair being divorced by Cherie in 1997 and publicly dating Naomi Campbell, such an event would not have quite the same significance here. While he is in office, the President embodies the Republic, and a sharp drop in Sarkozy's poll ratings since he began dating Bruni suggests that voters don't want to watch the Republic partying like Prince Harry.

France has had its share of flamboyant kings, and the only question that rattled Sarkozy at his press conference was from a Libération journalist who asked whether he was creating an elective monarchy. The accusation was bolstered a couple of days later by a passage in Bitton's book which has Sarkozy's ex-wife describing his entourage as "drunk on power" and taking themselves for "the princes of Paris".

His recent behaviour is certainly in character. Sarkozy did not attend any of Paris's elite academies; he qualified as a lawyer and entered politics as mayor of Neuilly. In that capacity, he found himself conducting the wedding ceremony of a beautiful young woman, Cécilia Ciganer-Albéniz.

Sarkozy struck up a friendship with the newlyweds and eventually married Cécilia himself, establishing a pattern – he is a man who single-mindedly pursues the woman he wants – which is now being repeated with Bruni. Indeed, the superficial physical resemblance between Carla and Cécilia is probably less important than Bruni's status as a former supermodel with a series of famous ex-lovers, which makes her the perfect trophy girlfriend.

Sarkozy claimed last week that he is as entitled to love and happiness as the man in the street. But the most compelling charge against him is that he is a shameless exhibitionist who has exploited confusion in France about the boundary between public and private life to assuage hurt pride.

For years, the French have congratulated themselves on not intruding into politicians' private lives, maintaining a reticence which has disappeared in most Anglophone countries. They have been shielded from some of the excesses of celebrity culture but their presidents' personal lives are still predicated on the antiquated assumption – shared by Jack Kennedy and Bill Clinton, among others – that power entitles them to sexual privileges.

All Sarkozy has done is to bring that assumption into the open, sacrificing his dignity into the bargain. There is nothing radical or modern about his conduct, and it will be harder in future for French politicians to protect their private lives, even if they are quietly dating someone who isn't in public life. But the biggest danger lies in one person unilaterally deciding to change the nature of a long-established institution. Lady Diana Spencer did it in this country, marrying into a family that was a figurehead, and transforming them, to disastrous effect, into worldwide celebrities.

It's a cautionary tale if ever there was one, but I doubt Sarko is in a mood to hear it. With more strikes looming and the homeless multiplying on the streets of Paris, the President of the Republic is showing his true colours: small man, Napoleon complex, big trouble.