PARIS—Jean-Luc Mélenchon, the former Trotskyite, far-left French presidential candidate, has often drawn comparisons with Bernie Sanders—including from himself. Like Sanders, he proved adept at tapping an authentic feeling of popular anger mixed with a youthful spirit of resistance and revolution.

At the head of his own “La France Insoumise” party (alternately translated as “Unsubmissive France,” “France Unbowed,” and “France Standing Tall”), he enlisted the support of France’s Communist Party, eschewed the Socialist Party primary, and played spoiler to the left wing establishment from the outside, with a nostalgic message that raged against globalized trade, a “neoliberal” European Union, and American hegemony.

He promised retirement at 60, a 32-hour workweek, a 90 percent tax on income above €400,000, a Keynesian stimulus plan, plus a permanent €100 billion increase in state spending, greater cooperation with Vladimir Putin, and a referendum on French membership in the euro and the E.U. if Germany refused to “renegotiate the European treaties.”

Though objectively much further to the left than Sanders, Mélenchon also seems to have attracted the French version of the “Bernie Bro,” the sometimes overly zealous Sanders supporters who toed a fine line between online activism and trolling of anyone critical.

Joann Sfarr, a political cartoonist, found that out the hard way: A few days before the first round of voting, he posted on Facebook (including in the form of cartoons) that after reading Mélenchon’s platform and discovering foreign and economic policy proposals that tilted towards Putin and away from the European Union, he had decided not to vote for him anymore.

As a result, his page and posts were thronged with hordes of aggressively pro-Mélenchon commenters, many of whom coordinated with each other in unofficial organizing rooms on the platform “Discord.”

Days after the first-round vote saw the far-left candidate garner 19 percent of the ballots, many of those voters are upset, and still vocally engaged. Except in a way that could spell disaster well beyond France’s hexagonal borders. Because nearly half of those who voted for Mélenchon in round one are promising to abstain from voting in round two.

The divisions between the 39-year-old Emmanuel Macron, running for his first elected office, and Marine Le Pen, who inherited leadership of the National Front (FN) from her father, could hardly be more more stark. And the existence of the European Union itself is at stake.

Despite that, for the past several days social media have exploded with a cascade of posts from French millennials insisting that Macron and Le Pen are equally bad, much like jilted Sanders supporters argued for months that Hillary Clinton was no better than Donald Trump. It was an absurd claim then, and should be easily debunked now with little more than a glance across the Atlantic. Nevertheless, it’s persisted, in part, thanks to the leader of les insoumis himself.

Mélenchon's behavior on election night was churlish.

“Mediacrats and oligarchs are rejoicing,” is how he began his speech to his supporters, before casting Macron and Le Pen as equally treacherous and refusing to pick a side.

For as long as the National Front has existed, mainstream French politicians, voters, and media have treated the party—born and steeped in an ideology of anti-Semitism, Islamophobia, racism, nationalism, and hate—as simply untouchable. Sacrificing when called upon, they have repeatedly constructed a "cordon sanitaire" around the FN, refusing to publish editorials by its leaders, and forming a "Republican Front" against it in 2002, when Jean-Marie Le Pen shocked the nation by advancing, as his daughter has just done, to the second round.

Then, Mélenchon had joined the effort to keep the FN cordoned off from the Republic's respectable politics. In a column in Le Monde titled “Stop This Race to the Abyss,” he left no lingering doubt about how he viewed the extreme right, and about the duty of left wing voters to stand in its path.

"How in good conscience could the left decide to count on others to protect what is so essential, by being unwilling to do something we think is undignified?" he had asked. "Not doing our Republican duty because we find it nauseating is to choose unprecedented collective risk over individual inconvenience."

Well, the Mélenchon of 2017 would do well to read the Mélenchon of 2002. As I write this, he has yet to make a declaration about who he will vote for in round 2, if indeed, he will vote at all.

What happened in the space of15 years? How did a defiant you shall not pass disintegrate into nothing more than bitterness and silence?

The normalization and breakout of the National Front is a multifaceted story. But an indisputable part of it was the party’s realization as far back as the 1980’s that it could construct appeal to the far-left, as well as the far-right.

As Tony Judt noted in his authoritative tome Postwar, “It was not by chance that the Front National often got its best results in districts that had once been bastions of the French Communist Party.” And as the historically powerful Communist Party gradually fell apart, the FN brought in far-left voters by mixing a statist, anti-globalization economic message with its ethno-nationalist one.

Rising radical right movements in Europe and the United States have accompanied a general breakdown in traditional political identification and party structure. In a first for the Fifth Republic, neither the mainstream left nor the mainstream right is present in the second round of the French presidential elections.

Things have a way of coming full circle. Over 200 years ago, the lines of traditional politics were born in France. “Those who were loyal to religion and the king,” explained Baron de Gauville, a deputy in the National Assembly at the time, “took up positions to the right of the chair,” with the revolutionaries separating themselves out on the left.

How fitting then, that the left-right divide may have died in France as well.

Over the past year, there have been numerous contributions towards understanding the new dividing line that is replacing it. Or more broadly, the “age of anger” as Pankaj Mishra puts it, that is sweeping the world. Each theory decrypts a little piece of the puzzle, and with its own terminology. The struggle between the “winners” and “losers” of globalization; between urban and rural areas; between cosmopolitans and nationalists; between the “anywheres” and the “somewheres.”

The Macron campaign, as Romain Champetier, a campaign official, told me, views the new landscape as “progressives and conservatives; or those who believe in “open, liberal, pro-European-based social and economic progress,” and those who “in a literal sense, are fantasizing about a past that France never really had.”

These dynamics are undeniably at play in the slow rise of the National Front. The party performed well in places racked by unemployment, and the smaller the town, the better Le Pen did there, compared to Macron’s dominance in cities larger than 200,000—a trend that holds even within departments that as a whole, swung for one candidate or the other.

And the identity component needs no extensive explanation, not when Le Pen on one side promotes a view of the nation as inextricably rooted in blood and earth, to be protected by strong borders, while on the other, Macron routinely extolls his hope that “every individual might find his or her place in France and in Europe.”

No other issue more neatly encapsulates the opposing camps of 21st century politics than “Europe” and what it represents—loss of identity for the right, “neoliberalism” for the left (never mind that nearly all of its policy goals, from stopping corporate tax evasion to fighting climate change, are all more effectively fought at a European level than a national one).

We’re looking at a fundamental contest between those who think the liberal international order basically works, but needs tweaks and reforms, and a mélange of revolutionaries on the right and the left who want to overturn it entirely.

For the far left too, has a romantic idea about borders. Where the right thinks that it can erect walls and thereby pockmark Europe with enclaves of homogenous national culture, the left fantasizes about shutting out the world in order to force the market to do what it wants. (This was the essence of Mélenchon’s domestic economic agenda, and the reason why, despite protests to the contrary, leaving the euro, and perhaps the E.U., would have been near necessities for fully pursuing it.)

All this has led to an often caricatured vision of the centrist Macron, drawn from his history as a banker and during his two-year stint as economy minister the architect of the loi travail, a highly controversial package of economic reforms that, among other things, allowed intercity busses to compete with the national railway operator, and permitted businesses in designated tourist zones to remain open on Sundays and until midnight, provided they paid employees double for working irregular hours.

Thus, for an important section of la gauche, a candidate whose actual policy platform lies somewhere to the left of Clinton and to the right of Sanders, came to be seen as the puppet of big finance and corporations, intent on the destruction of the French social model. (Macron, for his part, while a proponent of some labor market reforms and greater European integration, has not proposed any fundamental reductions to the French welfare state that has succeeded in lowering inequality to near-Scandinavian levels.)

Such reasoning has formed the basis for the justifications offered by those promising to vote for nobody in the second round.

The night of the U.S. election, one of my childhood friends posted on Facebook that he was choosing not to vote, because Hillary was going to win anyway, and that everyone criticizing him would see that he was right.

Unfortunately, moments of folly aren’t limited to one side of the Atlantic.

Says one Facebook commenter here in France, “I’m abstaining. If I could vote blank and have it count, I would, but I can’t. Sure the extreme right is fascist, but extreme finance is fascist too.”

And another, “Macron is a candidate put forward by banks, the media, and multinationals…people who vote for Hollande 2.0 in the second round should be ashamed.”

And finally, a third who explained his reasons to me in a long message,“Voting for Macron isn’t only legitimizing his ultra-liberal [in the classic laissez-faire economics sense] policies over the next five years, but rolling out the red carpet for Marine Le Pen in 2022, or even before.”

… Except that the before would be now. As in, 2017. And if, like me, you’re left dumbfounded by the idea that somehow allowing Marine Le Pen to take office in 2017 is the solution to preventing her from winning the election in 2022, don’t think about it too hard, because your brain might explode.

To be clear, there is a fundamental division among the revolutionaries who want to rage against the system. The left does have a long tradition of standing up to the National Front’s xenophobia. The vast majority of disaffected insoumis would never vote for Le Pen. But as the target narrows on “globalization” in its multiple forms, many of them won’t vote against her either, and the Burke-ian consequences of that choice—and rest assured, refusing to make a choice is making a choice—are inescapable. Just as they were for the United States.

Could they be decisive?

“Of course we are worried,” Champetier admitted to me, “It’s a big concern for a lot of people. But we are in the world, and having an anti-globalization project is not wanting to face reality. And people will realize that his program is not ultra-liberal like it has been caricatured.”

All polling suggests that this is Macron’s race to lose. But even if less likely than a Trump victory, a Le Pen victory remains possible in a low turnout environment, perhaps driven by a conviction that the ideological sacrifice of casting a reluctant vote can be avoided because faceless “others” will turn out against Le Pen anyway.

In its enthusiasm for youth and “centrism,” the foreign media has overlooked the fact that Macron, while surely popular with some, is merely the “lesser of all evils” for most of those who will cast a ballot on his behalf in the second round. As France 24 notes, “If one adds up the first-round tallies of all the candidates who either wished to quit the E.U. or had serious qualms about its ‘neoliberal’ slant, the result is a country split in half.” And the next president only needs 50 percent of the vote, plus one vote more.