UMP leadership race: The battle for Sarkozy's party
They have called it a "civil war" in France's UMP party. Certainly the rhetoric has been fiery.
Since Nicolas Sarkozy stepped back from front-line politics in the wake of his defeat in the May presidential election, his party has been leaderless - perhaps even rudderless.
The two men bidding to replace him have very different visions of which way the UMP should now be steered.
In many ways this is a carbon copy of the debate that preoccupies the bruised Republican party of the United States: whether to veer to the right as it seeks to recover from defeat or cling somewhat unconvincingly to the centre.
Francois Fillon, Mr Sarkozy's prime minister, is the favourite to succeed him.
In office he was the perfect foil to the exuberance of the former president - sober, more restrained and, at the end, more popular with a large section of the public.
As such. he is confident he can win back the voters who abandoned his party in May for the Socialists. In polls for this Sunday's vote, he is favoured to win. If he did, he would fight to run as the party's presidential candidate in five years' time.
His opponent Jean-Francois Cope is a different mix of right-wing values.
He is much more combative - not that dissimilar to Mr Sarkozy as it happens - and not ashamed to woo the voters attracted by the rhetoric of Marine Le Pen and the far-right Front National.
He would side with Mr Fillon on Europe and the economy but on immigration, on Islam, on the challenges facing the suburbs, he is far more provocative.
The magazine Le Nouvel Observateur claims the centrists are already packing their bags to leave if Mr Cope is elected. His supporters say he is much more in touch with the concerns of ordinary voters.
Last month, Mr Cope produced "A Manifesto for an Uninhibited Right", in which he claimed the gangs in the banlieues were fostering "anti-white racism". In fact, he tweeted an anecdote, about a child who had been robbed of his pastry by "thugs" who, Mr Cope claimed, were enforcing the Ramadan fast.
His comments have brought ridicule in some sections of the press. And this week the new Interior Minister, Manuel Valls, brought parliament to the point of uproar, claiming it was such talk by the right that had divided the country.
There are others within the UMP who think it has also split their party.
"Toxic and dangerous," said Francois Baroin, Mr Sarkozy's former finance minister who has given his backing to Francois Fillon.
And so, the vote this weekend will tell us a lot about where the base of this party is turning. Will it continue to be a party in the image of the one that was founded by Charles De Gaulle? Or something much further to the right?
The vote is open to around 300,000 UMP members. If Mr Fillon is elected even with a modest turnout, he and his supporters will take it as evidence that the rank and file want a more moderate party line.
Does it mean that whoever is elected will run against Mr Hollande in five years time? Not necessarily.
If Mr Fillon wins, then he would want the ticket. If Mr Cope wins, he has not ruled out standing aside for the return of the irrepressible Nicolas Sarkozy.
The former president is in buoyant mood but there is a problem: a judge in Bordeaux is now investigating his relationship with the l'Oreal heiress, Liliane Bettencourt.
There are allegations Mr Sarkozy personally accepted brown envelopes full of cash from the multi-millionaire's family to help fund his 2007 campaign - in return for massive tax breaks when he came to office.
Mr Sarkozy has previously denied all wrongdoing.
If proven, that would be the end. If proven. But all the talk in UMP circles is that he is preparing a comeback. And Mr Cope has signalled he would be only too willing to back Mr Sarkozy's bid for re-election.
The one big plus for the party, amid all this uncertainty, is that Francois Hollande's popularity is already on the wane as he fights to avert a recession. The new UMP leader must quickly rally the party to capitalise on the president's perceived difficulties.
But then it is not only the country's debt that must be tackled. The first job of the leader may well be to take charge of the UMP's own financial problems. According to the satirical weekly Le Canard Enchaine, the party has run up a 50m euro (£40m; $63m) deficit - there is debt wherever you look.