On the left, the surprise endorsement of former Socialist president Francois Hollande can’t hide the influence of far-left firebrand Jean-Luc Melenchon, who has dismissed antisemitism as a “residual” problem in France and who hasn’t ruled himself out as prime minister if his bloc comes top. Several planks of his 2022 presidential platform, whose cost was estimated at over €200 billion ($324 billion) by the think tank Institut Montaigne, have made it into the new alliance’s policies: a return to retirement at 60, down from 64; price controls; and a hike to civil servants’ pay that on its own would cost...