Mainstream left candidates unite with hard-left for mayoral runoffs.
Division among Socialists highlights internal party conflicts.
Jean-Luc Mélenchon’s France Unbowed plays a key role in the alliance.
Briefing: French Socialists split over alliance with hard-left party in mayoral runoffs
Strategic angle: Several candidates from France’s mainstream left have joined forces with Jean-Luc Mélenchon’s France Unbowed to boost their chances in mayoral runoffs, while others reject the alliance.