THREE YEARS ago the French Socialist Party was crushed into irrelevance. The party that supplied two modern presidents—François Mitterrand (1981-95) and François Hollande (2012-17)—and nine prime ministers, became as invisible in parliament as in public debate. Its presidential candidate in 2022, Anne Hidalgo, was beaten into a dismal tenth place, scraping together less than 2% of the vote. Its contingent in the National Assembly was swallowed up into a left-wing alliance dominated by the hard left’s firebrand leader, Jean-Luc Mélenchon. He engineered the downfall of the previous French government, under Michel Barnier, in December.