The response of Mette Frederiksen, Denmark’s centre-left prime minister, to being physically assaulted in a Copenhagen street was dignified and very human. “I’m not doing great, and I’m not really myself yet,” she admitted last week. The attack, in which she escaped serious injury, had left her feeling shocked and intimidated, she said. Frederiksen suggested her experience was the culmination of some broadly familiar trends: proliferating social media threats, increasingly aggressive political discourse, a divisive Middle East war. “As a human being, it feels like an attack on me. But I have no doubt it was the prime minister that...