If Europe’s cosseted political and media class had any sense—improbable, but bear with me—they’d recognize the magnitude of the disaster that befell them this past weekend in France. Instead, they believe that the legislative election result constitutes a win.

Superficially, it was a win. President Emmanuel Macron called the snap National Assembly election to try to stifle a challenge from Marine Le Pen ’s National Rally on the insurgent right. Her party performed well in European Parliament elections in early June, and Mr. Macron hoped to discredit her with a defeat at the national level.

His strategy has worked in one respect: Ms. Le Pen’s bloc has emerged as only the third-largest in Parliament. But to describe Ms. Le Pen’s loss as a victory for France or for Europe presupposes the alternative will be any better. Quite the opposite.

Conventional wisdom holds that an election triumph for Ms. Le Pen, if or when one comes, will pose a mortal threat to the Continent. Her Euroskepticism, the theory goes, would undermine French support for European Union institutions such as the euro currency and the single-market trade bloc. Her xenophobia would challenge European values.

Yet that parade of horribles is what France faces now from whatever left-leaning administration emerges following the election. The way in which the center and left defeated the National Rally is a major problem. Ms. Le Pen and her allies were by far the biggest vote-winners in Sunday’s second round, garnering around 37% of the vote compared with around 26% for the left and 25% for Mr. Macron’s coalition. The last two blocked Ms. Le Pen’s party by targeting winnable districts, which is a smart tactic in such a system. But the strategic error is that this has produced a National Assembly split three ways with no obvious governing mandate.

Whichever administration gets cobbled together from this chaos will govern from the left. It’s a bad sign that these parties seem to agree on only a few issues: expanding the government workforce and imposing a new wealth tax. Mr. Macron’s most important reforms to labor laws and pensions may be on the chopping block.

The European Union economy can’t function if its second-largest constituent (by gross domestic product, after Germany) has no realistic prospect of either growing or paying off its debts. Nor can France hope to contribute meaningfully to the North Atlantic Treaty Organization’s common defense without an economic jump start—if the left-leaning parties set to call the shots in Parliament even wanted to do so, which they don’t.

Ms. Le Pen’s opponents might retort that what was at stake in this election was France’s soul, not its economy. Ms. Le Pen’s party, they’d argue, with its hostility to immigrants and its history of antisemitism, poses an unacceptable threat to core French—and European—values.

This would be more credible if, to squeeze out Ms. Le Pen, Mr. Macron and centrist allies hadn’t been complicit in the success of France’s antisemitic far left. The embarrassing truth is that France Unbowed was the biggest election winner. That far-left party—founded by Jean-Luc Mélenchon , a sort of French Bernie Sanders—secured 74 seats, making it the largest party within the left-wing bloc. Mr. Mélenchon is notorious for his antisemitic comments, particularly following the Oct. 7 Hamas invasion of Israel (which his party called an “ armed offensive by Palestinian forces” rather than a terror attack).

Ms. Le Pen’s National Rally in the past was justifiably accused of antisemitism. Ms. Le Pen has launched a cleanup and has emerged as a vocal supporter of Israel . Perhaps she really means it. Perhaps she merely hopes to use a noisy display of philosemitism in her broader campaign to block Muslim immigration into France. But as a French sage once observed, hypocrisy is the tribute vice pays to virtue. If Ms. Le Pen is insincere, at least she knows where the virtue lies. Mr. Mélenchon doesn’t.

Were Mr. Macron more imaginative, he might have found in Ms. Le Pen a grudging helper for some reforms (her party belatedly made its peace with his pension overhaul) and an excuse for others such as an abandonment of costly net-zero climate follies. The political fusion with most promise these days—in Spain, Italy, Greece and perhaps in Germany and the U.K.—is a center-right that’s tough on immigration and aggressive on economic growth. A Macron-Le Pen condominium, as awkward as it sounds, might have delivered both results and some degree of popular legitimacy.

Instead, Mr. Macron continues to indulge a distaste for the insurgent right that looks increasingly aesthetic rather than ideological or practical. As a result, Europe may soon discover that a French government with Ms. Le Pen stuck on the outside is worse than an administration with her in it.