Former New York mayor Bill de Blasio has paid tribute to Helen Haines, the Australian MP who was attacked. In his tribute, he used the moment to send a pointed warning to Australians. His message was that the kind of political violence seen in the United States should never be allowed to happen in Australia. He praised the attacked MP while framing her experience as a sobering example. The tribute connected Haines's ordeal to the broader problem America faces with political violence. De Blasio's comments add an international voice to the concern many Australians have voiced since the attack. As someone who ran one of America's biggest cities, his appeal carries a sense of what political turmoil can do to public life.