Former Mass. Governor, and much cooler than usual Republican, William Weld, preceded him with a similar stunt over 30 years earlier when he dove into the Charles River in a business suit to demonstrate water quality improvements after new sewage treatment plant (created by Michael Dukakis) went online.

https://www.msn.com/en-in/money/topstories/why-did-new-york-mayor-zohran-mamdani-jump-into-a-public-pool-fully-clothed-breaking-the-pool-dress-code-tradition-explained/ar-AA26I9JY

…

First mayoral plunge in more than a decade

Mamdani became the first New York City mayor since 2013 to participate in the annual pool-opening tradition. The ritual had not been observed during the administrations of Eric Adams and Bill de Blasio, with Michael Bloomberg being the last mayor to take part.
Earlier this year, Mamdani had indicated that he "may commit" to reviving the tradition when asked about it by City reporter Katie Honan.

… more …

And his policies and leadership, are the future of the Democratic Party needs and wants.

After a game of stick ball.
Has chump ever done any typical New York things?
Who relates to everyday New Yorkers?
Hizzoner was born in Uganda and is a better everyday citizen than old man chump!
He also smiles !

That was one expensive jump. Shoes and all. He can probably write of as expenses.