CAMBRIDGE – In the French Republican party’s presidential primary on Sunday, François Fillon soundly defeated frontrunner Alain Juppé, winning close to 67% of the votes.

Two weeks ago, a landslide victory for the apparent underdog seemed out of the question. It had long been expected that Juppé, the mayor of Bordeaux and a former prime minister under President Jacques Chirac, would beat the other frontrunner, former President Nicolas Sarkozy, in a second-round runoff. Instead, Fillon, a former prime minister under Sarkozy, emerged from the first round with a commanding lead, winning 44% of the vote. The outcome was a humiliating one for Sarkozy, who received just a little over 20% support, and effectively ended his political career.

For many observers, the vote invoked the specter of June’s Brexit referendum and US President-elect Donald Trump’s victory earlier this month. Opinion polls placing Fillon as a distant third were proven wrong, partly because many voters seem to have made up their minds just days before the vote. Social media were also credited, again, with playing a key role. In the last debates before the vote, Fillon presented himself as a credible alternative to Juppé and Sarkozy.

With incumbent President François Hollande’s approval ratings below 5% – the lowest ever for a French president – the big question now is whether Fillon can beat far-right National Front leader Marine Le Pen in the second round of the presidential election in May 2017. Juppé was seen as a sufficiently "soft” candidate, who would provide an alternative to Le Pen for left-wing voters. Fillon, however, is much further to the right than Juppé, which means that left-wing voters might not see much difference between him and Le Pen, and could demand that a center-left third candidate enter the fray.

One contender is the centrist Emmanuel Macron, who says he will run but refuses to stand in the Socialist Party primary this January. Without major-party backing beyond his own En Marche!movement, however, Macron is unlikely to be able to muster the support needed to win the presidency (he currently has just 14% support). And, as a banker-turned-reformist economy minister under Hollande, Macron is an ideal target for Le Pen’s anti-elitist, anti-European rhetoric.

Beyond Macron, the left is struggling to put forward a credible candidate. Holland’s reelection chances are dismal; his loyal prime minister, Manuel Valls, is expected to announce his own candidacy this week, but is polling only marginally better than Hollande, at 9%. That leaves only the far-left Jean-Luc Mélenchon (13%) and the photogenic but waffling Arnaud Montebourg, whom Macron succeeded as economy minister.

If no leftist candidate makes it to the second round, voters on the left could cast their votes for "Republican unity,” as they did in 2002, when they handed Chirac a landslide victory over Le Pen’s father, Jean-Marie Le Pen. Leftist voters would have preferred Juppé, and will likely tolerate Fillon, but they comprised only 15% of total voters in the first round of the Republican primary, so they may not have the same impact in 2017 as they did in 2002.

Fillon’s political base is dominated by provincial, retired Catholic men, who turned out in force for both rounds of the primaries. Fillon’s supporters seem to be united in their opposition to gay marriage, and Fillon, as an avowed Catholic, was the most socially conservative candidate on offer. While Fillon does not want to revoke same-sex couples’ legal right to marry, he opposes granting them the right to adopt children.

Geographically, Fillon won almost everywhere outside of Juppé’s Bordeaux bastion, including the southern Mediterranean Provence-Alpes-Côte d’Azur (PACA) region, which was originally Sarkozy’s strongest base of support. But PACA is also the National Front’s stronghold, which means that Fillon will have to distinguish himself from Le Pen as a right-wing candidate, lest voters decide they would prefer the original to the copy.

There are a few areas where Fillon and Le Pen differ. For starters, Florian Philippot, one of Le Pen’s deputies, is openly gay, and Le Pen has been careful not to take a strong position on social issues. Fillon is also an economic liberal – and is often characterized as a French Margaret Thatcher – whereas Le Pen is a protectionist. And while Fillon wants to reduce the French civil service by 500,000, Le Pen favors a strong state.

Finally, Le Pen opposes France’s membership in the European Union and wants to return to the franc, while Fillon would prefer to delegate power back to national assemblies. Heading into the election campaign, Fillon may run on a pro-European platform, as evidenced by his pivot during the second-round debates, when he suggested that he favors forming a eurozone government.

Unlike Trump and the United Kingdom’s "Leave” campaign, the National Front already has a predictable core constituency, amounting to about one-quarter of the electorate. Its coalition of the old French far right and disaffected working-class voters will not arrive unannounced or defy expectations, as happened in the US and the UK.

Fillon, for his part, can probably muster the same level of support, and he may even be able to skim votes from Le Pen, given that around 8% of primary voters described themselves as National Front backers. What’s more, political Catholicism still appeals to many French voters, and the Church itself wants to lure Catholics away from the National Front and back into its more traditionally conservative fold. Meanwhile, a number of far-right organizations supported Fillon’s candidacy during the primaries, owing to his strong support for laws that would ban the burkini, a full-body bathing suit worn by Muslim women.

Given the current political field, Fillon will most likely face Le Pen in the presidential election’s second round next May. Polling after Fillon’s victory put his support at 26%, with Le Pen backed by 24% of respondents. Fillon, however, is projected to win the second round with 67% of the vote.

We have been here before, and that second-round projection is based on "Republican unity,” which might not hold. Left-wing voters, put off by Fillon’s liberal economics and social conservatism, might stay home. Given pollsters’ massive predictive failures elsewhere this year, no one should count on them to turn out until the votes themselves are counted.

Hugo Drochon, who teaches politics at the University of Cambridge, is the author of Nietzsche’s Great Politics

Copyright: Project Syndicate.