All eyes in France are on the right-wing nominating contest, whose winner is expected to go on to take the presidency in May in a duel with far-right leader Marine Le Pen.
Former president Nicolas Sarkozy, ex-premier Alain Juppe and five other candidates will compete in the first round on Sunday, with the two poll toppers going into a run-off on November 27.
Trump's stunning ascent to the White House loomed large over the last of three debates among the seven candidates.
Sarkozy, who is running neck-and-neck with Juppe in polls, said a more isolationist America created "a fantastic opportunity for France and Europe to re-establish a leadership role" on issues including security in the Mediterranean and the reform of the UN Security Council.
"The next five years will mark the return of France and Europe to the international scene. America won't be there to put us in the shade," he said.
Juppe said the Trump era heralded a triple "shock" -- in the areas of trade, defence and the environment.
A return to protectionism would be "a tremendous regression", Juppe said, while warning Europe against being "naive" in its dealings with the United States.
Responding to Trump's campaign threat to help NATO allies only if they paid their way, Juppe said EU members needed to speed up plans for greater defence cooperation -- a proposal backed by most of his rivals.
Trump's win has caused jitters in France, where Le Pen has seized on it as evidence that she could debunk the polls and take the Elysee Palace on a similar anti-establishment platform.
Socialist Prime Minister Manuel Valls admitted during a visit to Berlin on Thursday that it was "possible" that Le Pen could win the election and warned against ignoring the "danger" of the far right.
US-style 'hangover'
"I don't want us to wake up with a hangover, like the Americans, in six months' time," the sole female candidate in the right-wing primary, Nathalie Kosciusko-Morizet, said during the debate.
Thursday's debate was restrained in tone but sparks flew when Sarkozy was quizzed about fresh claims that he received millions in funding from the late Libyan leader Moamer Kadhafi towards his 2007 campaign.
Sarkozy had no answer for the question, which he termed "disgraceful".
Polls show the allegations having little impact on his campaign, with the ex-president closing in on Juppe, who has led the race for the past two years.
An Ifop survey on Thursday put them both at 31 percent, ahead of the reform-minded Fillon, up seven points in two months to 27 percent.
In the run-off Sarkozy is shown as losing to either Juppe or Fillon. If Juppe and Fillon are the two finalists Ifop predicts a dead heat.
Sarkozy has emphasised his tough-guy credentials, saying it makes him a better choice to handle Trump than the mild-mannered 71-year-old Juppe.
Both he and Fillon welcomed the prospect of a rapprochement between Washington and Moscow under Trump.
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'Cold war' no more
"The good news" of the US upset, Sarkozy said, was that it spelt an end to the "totally counter-productive climate of cold war between the United States and Russia."
Both Sarkozy and Fillon have pledged to dramatically curb immigration following a wave of jihadist attacks.
Bordeaux mayor Juppe, accusing Sarkozy of aping Le Pen, has campaigned as a unifier.
"To succeed we have to come together. For that our diversity must be respected," he said Thursday.
As the right prepares to pick its nominee the ruling Socialists are in disarray.
On Wednesday, Hollande's former star economy minister Emmanuel Macron became the latest to repudiate his mentor, announcing a bid to become president even though Hollande himself has yet to say whether he will seek a second term.
