(CNN) Hillary Clinton said Wednesday she is "very supportive" of a plan by the mayor of Philadelphia to tax soda in order to pay for universal pre-school.

Clinton was speaking at a forum in Philadelphia hosted by the Mothers of the Movement, a gun control advocacy organization, and discussed replacing the "school to prison pipeline" with a "cradle to college" pipeline when the soda tax proposal came up.

"It starts early with working with families, working with kids, building up community resources -- I'm very supportive of the mayor's proposal to tax soda to get universal pre-school for kids," Clinton said. "I mean, we need universal pre-school. And if that's a way to do it, that's how we should do it."

In early March, the Democratic mayor of Philadelphia, Jim Kenney, introduced a plan to tax soda at three cents per ounce in order to fund a universal pre-K program.

But Clinton and Kenney may discover -- like politicians before them -- that even the best of intentions can't protect the mayor's proposal from the tricky politics of a soda.

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