WASHINGTON — Public charter schools — caught between growing Democratic disenchantment and a Trump administration shift toward private schools — are preparing for political battle, as the long-protected education sector finds itself on the verge of abandonment.

Betsy DeVos, the education secretary, proposed major changes this month to a federal education fund that for decades has driven growth of charter schools, which typically are run independently but funded publicly and available, often through a lottery, to any child in a school district. In President Trump’s budget proposal for the fiscal year that begins in October, the stand-alone charter schools fund would be dissolved into a broad educational block grant to the states, leaving charters to fight for money with competing educational priorities.

Presidential budgets usually hold little weight, especially when the House is held by the opposition party. But for charter schools, the Trump administration’s shift in emphasis toward private school support comes at a precarious time — Democratic lawmakers have targeted the same federal charter fund.

Last year, the Democratic-led House appropriations subcommittee that oversees the education budget sought to cut the federal charter school fund by $40 million, though funding ultimately remained flat from the year before. This year, charters are bracing for the House to try to zero it out altogether.