French President Emmanuel Macron hoped that his snap election would compel the French citizenry to grasp the stakes in the apparently relentless rise of Marine Le Pen’s neofascist National Rally (RN). The idea sort of worked, just not in the way Macron intended.

The most important result was that four left parties came together in a New Popular Front. First, they agreed to run a single left candidate in every district. Then, in the second round, the left and center mostly agreed to withdraw candidates who placed third, to unify the anti-RN vote.

The surprising result was that the left coalition placed first with 182 seats, the Macron center came in second with 163, and the RN, which had gained the most votes in round one, was third with 143. Simple arithmetic gives the left plus Macron’s party 345 seats, well over a majority in the 577-member National Assembly.

But politics is not that simple. The biggest winner on the left was Jean-Luc Mélenchon’s far-left La France Insoumise (France Unbowed) party, with 74 seats. Mélenchon is a maximalist, and now considers himself in the role of kingmaker. Macron detests him. Beyond the hard core of his own loyalists, Mélenchon is widely considered a connard (asshole).

When the projections were announced, Mélenchon demanded that Macron appoint a prime minister from the popular front. "The president has the power, the president has the duty to call on the New Popular Front to govern," Mélenchon said Sunday night.

The leader of that government would presumably be Mélenchon himself or a close ally—clearly a nonstarter for a center-left coalition. The practical question is whether Mélenchon would direct his deputies to vote against the appointment of a prime minister from the moderate left. For now, it certainly looks that way.

So the left’s all-too-characteristic factionalism and personal vanity could well deny a remarkable outcome that looked to be unattainable as long as Macron was president: a center-left governing coalition led by a left prime minister on behalf of a progressive program.

If Mélenchon’s blocking does succeed, Macron is then left to cobble together some kind of governing majority. That could take weeks. It might include other components of the New Popular Front, namely the Socialists and Greens, Macron’s own party and its allies, and elements of the badly fragmented Republicans, the onetime Gaullist party, who took 45 seats.

Macron could get to a bare numerical majority in that fashion, but it’s anybody’s guess who the prime minister might be or whether the majority would hold. The result would be a period of instability reminiscent of the postwar Fourth Republic, which was notable for shifting coalitions and short-lived governments. There were 21 governments in the Republic’s 12 years.

The Fourth Republic ended in 1958, with the return of Charles de Gaulle, who created a new constitution that was overwhelmingly approved in a popular referendum. It provided for a strong executive. The one glitch that de Gaulle didn’t anticipate was what would happen when the executive and legislative branches were from different parties, so-called cohabitation. That has happened three times before, in 1986–1988, 1993–1995, and 1997–2002, but never to the current degree.

The French far right is down but not out. If the center-left fails to govern, Le Pen is likely to come roaring back.