Mr. Kenney is taking a different political tack. Instead of the usual eat-your-vegetables pitch of public health reformers, he is offering Philadelphians something delicious: a giant pot of money to fund popular city projects. He says his soda tax could raise more than $400 million over five years, enough to fund not just universal preschool, but also renovations to local libraries, parks and recreation centers; “community schools” that wrap social services with education; and cash for the troubled municipal pension program. He is not using the word obesity, or suggesting that people should drink less soda.

His tax would raise the price of a 20-ounce bottle of soda by 60 cents, an increase likely to make some shoppers think twice. But when asked about the health benefits of the tax, he says, “There’s really serious health benefits in pre-K.”

In other words, this soda tax isn’t for the nanny state; it’s for the needy state. Governments are starting to think of soda taxes as the next sin tax — an untapped source of revenue that could help with other things.