Hillary Clinton and Bernie Sanders have a new issue to disagree about: the wisdom of a soda tax.

A tax on sugary soft drinks, like the one proposed in Philadelphia and endorsed by Mrs. Clinton last week, divides the left. It can be seen as achieving an admirable public health goal of less sugar consumption or as a very regressive tax that falls more on the poor than the rich, since the poor tend to drink more soda.

While not the biggest issue the two candidates have tussled over, it is one that may reverberate across the country in coming years as more cities and states use the tax to raise revenue or improve citizens’ health.

Last week, Mrs. Clinton became the first presidential candidate to explicitly endorse a tax on sugary drinks. At a Philadelphia event Wednesday, she said a proposal there to use a soda tax to fund universal prekindergarten was a good idea.

“It starts early with working with families, working with kids, building up community resources,” Mrs. Clinton said, according to a CNN report. “I’m very supportive of the mayor’s proposal to tax soda to get universal preschool for kids. I mean, we need universal preschool. And if that’s a way to do it, that’s how we should do it.”