A lot of people went to bed on the night of November 8, 2016, confident that they would wake up to news of President-elect Hillary Clinton’s election victory. This is not, of course, what happened. Donald Trump’s stunning win confounded pollsters and pundits alike, much as had the UK’s decision to Brexit months earlier.

Political unpredictability has continued apace in 2017, and France’s presidential election represents an early test of whether the nationalistic tremors of 2016 will continue to haunt liberal democracy in its heartlands. One thing’s for sure: no-one can confidently predict the results of this contest. But to borrow a phrase, there are some known unknowns to brush up on ahead of time.

How does France elect a president?

Presidential elections in France are a two-step process, with the top two candidates from this Sunday’s first round progressing to a head-to-head run-off a fortnight later – which means that, whatever happens, we won’t know who’ll become France’s next president on Sunday, but we know who won’t. The two-stage system aside, the process is quite straightforward – the candidates with the largest vote totals progress.

So who’s in the running?

In recent years, two main parties have dominated French politics: the left-wing Socialists, and the center-right Republicans. The current president is Socialist François Hollande, who announced last year that he would not seek re-election, in large part due to staggeringly low approval ratings, which hit an eye-popping low of 4% (not a typo!) late last year.

As in any election without the incumbent running, the field is wide open this year – albeit to an extent unprecedented in French politics, for several reasons. First, with or without Hollande, France’s Socialist party is in disarray: similar to Democrats in the US and the UK’s Labour Party, it is riven by in-fighting between left wing forces and more centrist impulses.

This has served to fragment the electorate. The official Socialist candidate, Benoît Hamon, is struggling under the weight of his predecessor’s unpopularity. Meanwhile, two former Socialist ministers, Jean-Luc Mélenchon and Emmanuel Macron, have each seized chunks of the party’s traditional vote from the left and the right with their own new movements, Unsubmissive France and En Marche!, respectively.

The right wing has also splintered. The National Front, led by Marine Le Pen – the daughter of Jean-Marie Le Pen, who scored a place in the run-off election in 2002 – has seized on antipathy towards Muslim immigrants to lead many first-round polls this year. Meanwhile François Fillon, the Republican candidate, is riven by allegations of financial impropriety relating to salaries given to members of his family, which have threatened to upend his candidacy.

OK, so it’s a broad field. But who’s going to win?

It’s very hard to predict who will make it through to the run-off – let alone win – but right now there are four viable candidates who, polls suggest, each clustered at between 18% and 23% of the vote. Mélenchon, with a radically leftist agenda, has been gaining recently at the expense of Hamon, and is running at around 18%, for what would be a close-fought fourth. Fillon has resisted calls – even from among his own party – to drop out, and his support seems to have stabilized, as he is currently running in a close third. Macron and Le Pen, meanwhile, have been trading the lead for the last few weeks, with each averaging around 23% of the vote.

The state of the French presidential polls at the time of writing. (Wikipedia)

The results of the run-off will depend, of course, on who makes it through. As things stand, one candidate – Macron – would win his head-to-head with each of the other three viable candidates, while another – Le Pen – would lose all of hers. (Mélenchon beats Fillon in the least-likely match-up.) But polling the run-off accurately is difficult while other candidates remain in the race, particularly when three out of the four leading candidates represent parties who have never won the presidency. In particular, if Fillon continues his comeback and makes it through to the run-off against Le Pen, the achingly familiar prospect of an experienced but scandal-plagued establishment candidate losing to a xenophobic outsider seems plausible.

How important is this election?

In a word, very. In constitutional terms, the French presidency represents something of a middle way between a mostly-symbolic head of state like the German presidency, and the powerful executive in the American system. Compared with America, periods of “cohabitation” – where one party controls parliament while another occupies the presidency – have been relatively rare, and in these instances, the president tends to take a back seat.

But one area in which French presidents have the most control is in foreign affairs, and France’s election this year represents, in a certain sense, another referendum on the European Union. Only the far-right Le Pen has vowed to leave the Euro currency, but both she and Mélenchon have adopted the fateful promise made by Britain’s David Cameron to renegotiate France’s relationship with the EU and put the resulting settlement to a formal referendum vote.

Meanwhile, Le Pen and Russian President Vladimir Putin have been open about their mutual respect, and Fillon is also notably more comfortable with Russia than other Republican figures – while Macron, the only avowedly pro-European candidate has been hit with a barrage of cyberattacks and fake news. Again all this sounds familiar, perhaps that’s because it is.

Both politically and geographically, France is much more central to the European project than Britain ever was, so a rebuke by voters would represent a much more existential threat to the Union – creating precisely the kind of instability that Russia’s Putin is said to want.

What else is there to know?

The polls are changing daily, and the election is now too close to call, according per multiple outlets. While this uncertainty creates volatility, in everything from markets to geopolitics, at least pundits and the public alike are more prepared for multiple outcomes than they were on the mornings of June 24 and November 9, 2016, when British and American voters created political earthquakes. It’s always useful to know what you don’t know.