“It’s hard to do a ban on cigarettes because you’re taking something away from people they have and are using. Once you have something, you hold tight,” said Richard Daynard, a Northeastern University law professor who focuses on tobacco issues.

Better, he said, to bar people from having a product in the first place. He is intrigued by legal efforts in Singapore and a handful of other countries to ban sales of tobacco to anyone born after a certain year — 2000, say. That would be constitutional, he said. The question is: Would our culture accept it?