ATLANTA — The night before Democratic presidential candidates took to a debate stage here last week, black and Latino charter school parents and supporters gathered in a bland hotel conference room nearby to make signs they hoped would get the politicians’ attention.

“Charter schools = self-determination,” one sign read. “Black Democrats want charters!” another blared.

At issue is the delicate politics of race and education. For more than two decades, Democrats have largely backed public charter schools as part of a compromise to deliver black and Latino families a way out of failing district schools. Charters were embraced as an alternative to the taxpayer-funded vouchers for private-school tuition supported by Republicans, who were using the issue to woo minority voters.

But this year, in a major shift, the leading Democratic candidates are backing away from charter schools, and siding with the teachers’ unions that oppose their expansion. And that has left some black and Latino families feeling betrayed.