PARIS — The incumbent leader of France’s Socialist Party, Olivier Faure, was reelected by a razor-thin margin in a contest that exposed a serious split among the center-left movement on electoral strategy.

Faure, a lawmaker representing a constituency just east of Paris, defeated Rouen Mayor Nicolas Mayer-Rossignol with just 50.9 percent of the vote. While official figures have not yet been released, it appears the election came down to just a few hundred votes.

The Socialist Party has been bitterly divided over Faure’s decision to join pan-left coalitions during the last two general elections. Before then, the party had suffered a string of crushing defeats running under its own banner.

Faure has argued that these alliances allowed the party to rebuild and regain parliamentary seats, but his critics say the Socialist brand is vanishing in the shadow of Jean-Luc Mélenchon — the popular but divisive hard-left figure who has performed better than any other left-wing candidate in the past two presidential elections.

In a post on X, Faure promised to continue to root his party “at the heart of the left.”

Mayer-Rossignol, who campaigned against Faure’s strategy and vowed to aggressively take take charge of any future coalition on the left, conceded shortly after the results were made public early Friday morning.

During the last leadership contest in 2023, which also featured Faure and Mayer-Rossignol, both camps disputed the close results for several days.

Alliance-building is sure to remain a central issue for the left. Local elections are scheduled across France next year and the next presidential election will follow in 2027. President Emmanuel Macron will also soon regain the authority to dissolve parliament, though he and his office have shot down reports that he would do so in the coming months.