Liberal politicians outside the US have watched Zohran Mamdani’s election win as New York mayor with interest, with some saying it offers lessons in how to combat the rise of rightwing populism around the world. The London mayor, Sadiq Khan, congratulated his US contemporary. “New Yorkers faced a clear choice, between hope and fear, and just like we’ve seen in London, hope won,” he wrote. Khan was also the first Muslim mayor of his city and has attracted similar hostility from Donald Trump. Unlike Mamdani, however, Khan is a career politician rather than a newcomer. Another Labour politician, the MP...