Terrible tragedies test leaders to the full. Anyone watching from afar must be impressed with the way in which Jacinda Ardern has dealt with the aftermath of the Christchurch horror. Ardern has kept her shocked population regularly updated, walked the talk in her embrace of the country’s Muslim community, and flagged policy changes in relation to New Zealand’s gun laws. She has radiated deep compassion while publicly holding her emotions under control. Friday’s atrocity would inevitably hit Australians hard, given the two countries’ “family” relationship. But we’ve been dragged much closer to it because the white supremacist perpetrator is an…