Zohran Mamdani is reveling in what he calls a “new era” for New York City. He was officially sworn in just after midnight Thursday, but politicians and other supporters gathered at City Hall in the afternoon for a larger ceremony. Mamdani is the city’s first Muslim mayor, its first of South Asian descent and the first to be born in Africa. At 34, he is also the city’s youngest mayor since the late 19th century. The democratic socialist takes office after a historic campaign made “affordability” a national buzzword across the political spectrum. U.S. Sen. Bernie Sanders administered the public oath of office to Mamdani today.

Zohran Mamdani has promised to transform New York City government when he becomes mayor. Can he do it? Mamdani, a 34-year-old democratic socialist, already faces intense scrutiny, even before taking office in one of the country’s most scrutinized political jobs. Republicans have cast him as a liberal boogeyman. Some of his fellow Democrats have deemed him too far left. Progressives are closely watching for any signs of him shifting toward the center. On Jan. 1, he will assume control of America’s biggest city under that harsh spotlight, with the country watching to see if he can pull off the big promises that vaulted him to office and handle the everyday duties of the job.