Open this photo in gallery: Shannon Seban, a legislative election candidate for the camp of President Emmanuel Macron, campaigns, in the Paris suburb of Ivry-sur-Seine, on June 25.John Leicester/The Associated Press Amid market stalls heaped with fresh foods, the shopper walked past the young candidate campaigning for votes in France’s high-stakes and torrid legislative election but then paused and doubled back to give Shannon Seban a piece of her mind. What happened next is becoming depressingly familiar for the 28-year-old candidate, who is Jewish and says she’s increasingly on the receiving end of antisemitism that has surged as a hot-button...