Tonight on stage in Denver Hillary Clinton, one of the most accomplished practitioners of the fine art of political deception, will pull off the biggest stunt of her career so far.

In her speech to the Democratic convention Mrs Clinton will have warm words for Barack Obama. She will pledge herself to work for his election in November. She will urge her campaign supporters and the millions who voted for her in the primary to bury their differences and throw their support behind the nominee. She will, no doubt, describe herself as humbled.

Don’t believe a word of it. There may be strenuous efforts to keep the tensions between the Clinton and Obama camps below the surface here in Denver, but they are as raw and powerful as they have ever been.

There has been loud grumbling among the Clinton team about the way that Mr Obama went about picking his vice-presidential nominee last weekend. They think that it was disrespectful of him not to have considered Mrs Clinton more seriously for the job. They are furious that he failed to consult Bill Clinton, the man who ran twice successfully for the presidency, for advice on the pick.

But most of all, many of them still have not come to terms with the arithmetical reality that they lost.

To be fair, it is not simply naked personal ambition that lies behind the rancour. The Clinton people have armfuls of polling evidence now that Mr Obama is failing to appeal to many of the voters that Mrs Clinton won in the primary campaign.

A CNN poll conducted at the weekend indicated that 27 per cent of Mrs Clinton’s supporters in the primary would vote not for Mr Obama in November but for John McCain, the Republican candidate. That figure is up from 16 per cent a month ago.

This number is causing alarm within the Obama camp. They know that it is almost impossible for him to win the presidency without those voters. That explains why the candidate’s team have swallowed their fears of turning the convention into a Clinton show and agreed to such a prominent role for the First Family of the Democratic Party.

Tonight, before she addresses the convention, Mrs Clinton will be the subject of a short biopic, a soft-focus documentary account of her many virtues – the sort of thing reserved usually only for the presidential nominee or for some party grandee in ebbing years.

Tomorrow, the night that should be dominated by Joe Biden, the vice–presidential nominee, will surely be overshadowed by another barnstorming performance by Mr Clinton. Expect, by the way, the former President, unlike his wife, to be somewhat less than generous about Mr Obama. Aides say that he continues to smoulder more pungently about what he perceives to be the slights on him from the Obama campaign. He is miffed about the way he believes that Mr Obama’s folk implicitly accused him of racism and he is really angry about the way the Democrat campaigned without paying much credit to the Clinton presidency.

The formal roll-call vote for the presidential nomination is also tomorrow. Mrs Clinton is making a very public effort to downplay this event – magnanimously releasing her delegates to vote for Mr Obama if they wish. But if it goes ahead it could still provide an opportunity for Clinton hardliners to express their raw feelings.

The trick, of course, for the Clintons this week is to appear to be doing all they can to support the Democratic nominee, while secretly hoping and praying that he loses. Nothing that Mrs Clinton says in the next few days must be allowed to be interpreted as undermining Mr Obama.

There is a growing conviction among some of her key supporters that their contention in the primary campaign – that Mr Obama could not win in November – is being underlined in Republican red ink every day.

They – and the Clintons – would like nothing better than to be proved right the day after the November election: the day that the next Clinton campaign for the presidency begins in earnest.

Times Recommends

• Tehran cannot live up to its rhetoric
• The new unicycle that will ‘change the world’
• We cannot wish away Iran’s bomb