PARIS/BORDEAUX (Reuters) - Francois Fillon fought off a rebellion that had threatened to end his candidacy for the French presidency on Monday as party leaders swung behind the center-right former prime minister despite allegations that he had misused public funds.

Hours after party heavyweight Alain Juppe ruled out challenging Fillon, the conservative Republicans’ party leadership unanimously backed their beleaguered candidate, Senate leader Gerard Larcher said.

“The Republicans are united around Francois Fillon,” Larcher told reporters, after telling fellow party officials behind closed doors: “The debate is over”. The conservatives are re-launching Fillon’s campaign, party chief Bernard Accoyer added.

Less than 50 days from the election, opinion polls show 63-year old Fillon - once the election frontrunner - crashing out in the first round. They also show an overwhelming majority of French wanted him to drop out of the election.

But despite growing calls within the party against his candidacy, challengers failed to convince Fillon to step down voluntarily and could not agree on an alternative candidate.

The allegations that he paid his wife lavishly from taxpayers’ funds for doing little work as his parliamentary assistant have badly damaged Fillon and also rattled foreign investors who fear it could boost far-right leader Marine Le Pen’s election chances. Fillon denies any wrongdoing.

The euro fell on Monday after Juppe announced he would not challenge Fillon.

“WHAT A WASTE!”

Juppe, a former prime minister like Fillon, said he had considered stepping in but decided against it because he felt his camp was too divided for him to be able to unite it.

“As for the right and the center, what a waste!” Juppe said of his party’s chances in the election.

Before the scandal, Fillon had been favorite to return the right to power against a backdrop of high unemployment and sluggish growth under Socialist President Francois Hollande.

But now his predicted poor showing in the first round on April 23 would leave centrist Emmanuel Macron to face Le Pen in a runoff on May 7. Macron, 39, a former investment banker who has never run for elected office, is forecast to win.

Polls have shown that Juppe, who is 71 and lost to the more right-wing Fillon in their party’s primaries, would have made the second round comfortably.

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They also indicated that Juppe would have beaten Le Pen more easily in the second round than Fillon, given his greater appeal to centrist voters opposed to the anti-euro, anti-European Union, anti-immigration stance of the National Front candidate.

“Francois Fillon... had a boulevard (to the presidency) in front of him,” Juppe said in the city of Bordeaux. “The instigation of judicial investigations against him and his defense based on a supposed plot and political assassination have brought him to a dead end.”

Fillon has complained of media and judicial bias against his candidacy that he says amount to a “political assassination”.

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Juppe’s uncharacteristically harsh words for Fillon, whom he called obstinate for staying on, exposed the depth of frustration within France’s mainstream political right, which has never failed in postwar history to reach the second round of a presidential election but is now forecast to do so.

But Fillon was unfazed, telling the emergency meeting of party officials: “It is time for everybody to get their act together and come back to their senses.”

“I call on all women and men of good will to rally, to respect the message our voters sent during the primaries and to unite behind my candidacy, which is the only legitimate one,” he said, according to a transcript of his speech.

Fillon revealed last week he was to be summoned by a judge later in March with a view to being put under formal investigation.