New Delhi, Nov. 6 -- Zohran Mamdani is not the sort of person who tends to get elected in America: he is not just a young immigrant of Muslim faith, he has the temerity to describe himself as a 'Socialist'-qualified with 'Democratic.' Yet, he has been elected mayor of New York City (NYC), the nerve centre of American and global finance, at a time when nativist politics of the kind promoted by President Donald Trump has many Americans in its thrall.

This is not, let's be clear, the start of sweeping change in the US. Mamdani had several special factors in his favour: New York is America's most cosmopolitan city, it has long been a Democratic stronghold and the record of his opponents was hardly inspiring; one had taken many failed shots a...