French presidential candidate Francois Fillon gets makeup applied | Thierry Zoccolan/AFP via Getty Images French presidential debate: What to watch for The focus will be on front-runners Marine Le Pen and Emmanuel Macron, but 3 other candidates will try to steal the spotlight.

PARIS — France's presidential election campaign goes primetime on Monday at 9 p.m.

The five top contenders for the presidency will face off for the first time in a TV debate that could send the campaign spinning in a new direction.

Most attention will be on former Economy Minister Emmanuel Macron and far-right leader Marine Le Pen. They are predicted to occupy the top two places in the first round of the election on April 23, with Macron forecast to win the runoff vote two weeks later. The two antagonists — she is a nationalist and statist; he is a pro-EU social democrat — have never before faced off directly. By watching them, voters will have the first chance to compare their almost diametrically opposed visions for France's future.

Broadcast by TF1, the show will last for at least 2.5 hours and probably longer, if previous debates are a guide. Each candidate in turn will have two minutes to answer a question on one of three themes: France's welfare model, its economy and its role in the world. Time will also be allotted for brief rebuttals, but the format is not optimized for a back-and-forth between the candidates.

The candidates will be sitting in a circular formation, at the apex of which will sit journalists Anne-Claire Coudray and Gilles Bouleau.

POLITICO Europe will run a live blog on the debate starting at 7 p.m. Paris time.

Here's what to watch for:

Emmanuel Macron: Test of presidential gravitas

Aged 39, Macron will be the youngest candidate on stage by some distance and he has only a few years of front-line political experience. He can take comfort from surveys showing a narrow majority of French people believe he has what it takes to run Europe's second-biggest country. But the former investment banker will have to prove he has enough authority to appear statesmanlike in front of veteran politicians such as François Fillon, a conservative former prime minister, and the sharp-tongued leftist Jean-Luc Mélenchon.

Macron's main antagonist is likely to be Le Pen. The National Front president is accustomed to attacking him as a member of a corrupt elite and a holdover from President François Hollande's unpopular presidency. Macron will have to stand by the argument that he is a "populist" candidate while striking back at Le Pen — without making the mistake of sounding disdainful.

Marine Le Pen: Needs to reassure voters about her program

The National Front president is as popular as she has ever been despite several legal probes into her party's finances. However, Monday's round-robin format will force candidates to talk less about their rivals' perceived failings and more about their own presidential programs.

In this regard, Le Pen still has many voters to win over. Polls show that while a majority believe she can bring change, most also find her program to be worrying. Le Pen will have to try to reassure those discomfited by her lack of executive experience and her proposal to hold a referendum on France's membership of the European Union. The National Front party chief recently adapted that proposal, suggesting France should keep the euro alongside the French franc after a withdrawal. Expect rivals to hone in on such vacillations, and seek to undermine Le Pen as being unfit for the job.

François Fillon: Last chance for a big comeback

On Monday night, the beleaguered ex-prime minister will get a chance to show he can still be elected president. Battered in the polls over repeated scandals linked to payments of public money to his wife and children, and more recently to expensive suits he accepted as gifts from a well-known lawyer, the conservative candidate is looking for a comeback.

He knows that a live TV debate is just the place to convince voters that he remains the candidate best-suited to the presidency. He stunned viewers with a strong showing in a conservative primary debate last year — after seeming so down-and-out that newspapers had given up on interviewing him. But the challenge Fillon faces this time is different: He no longer needs to show voters that they should pay attention to him; they're already doing that, thanks to daily articles about his scandals. He must convince a majority that he is worthy of their trust.

Expect Fillon to emphasize his experience as a statesman to set himself apart from all others onstage.

Jean-Luc Mélenchon: Time to prove who rules the left

For the leftist firebrand Mélenchon, Monday's debate is a chance to jumpstart a campaign that has been losing steam in the polls. Mélenchon must prove to left-wingers that he is offering something different from Benoît Hamon, the winner of a Socialist primary election and a rival for the far-left tranche of votes. The two men — both anti-free trade, both proposing radical institutional change — have so far failed to reach agreement on whether one should drop out and support the other. Of the two, Mélenchon is by far the more compelling speaker, with a ruthless wit to match. But to prove that he deserves to be crowned as King of the Left, he must avoid trying to destroy his rival — a fine line to tread for more than two hours.

Benoît Hamon: Needs to show he's playing to win

The winner of a Socialist primary can feel cheerful thanks to encouraging polls and a big rally on Sunday that garnered much favorable coverage. Hamon is beating Mélenchon in an undeclared contest for supremacy over the radical left. But the former education minister must now prove that he is not merely trying to position himself as the next leader of the Socialist Party, but making a determined push to get elected president. To broaden his appeal, Hamon must fight back against criticism that some of his proposals, like a guaranteed basic income for all adults, are unrealistic and opportunistic. As he tries to move toward the center, onto Macron's terrain, a fearsome opponent will challenge him for rightful ownership of the left: Mélenchon.