A woman holds one of three medications she uses to treat her HIV. Medicaid has helped to stem emerging threats like HIV/AIDS, and advocates worry it will be hinder under Republican plans.

WASHINGTON — Under the GOP’s vision for overhauling Medicaid, the program could struggle to afford expensive breakthrough treatments, cutting off its recipients from the latest medical innovations, warn policy experts and patient advocates.

Republican plans to institute some kind of Medicaid spending cap would mark a fundamental change in the nature of the program. Right now, the federal government (with mandatory matching funds from the states, which actually administer Medicaid) pays whatever costs recipients incur for care that is covered by the program.