This analysis examines the potential impacts on states and Medicaid enrollees of eliminating the 90% federal match rate for the Affordable Care Act (ACA) expansion. Eliminating the federal match rate for adults in the Medicaid expansion could reduce Medicaid spending by nearly one-fifth ($1.9 trillion) over a 10-year period and up to nearly a quarter of all Medicaid enrollees (20 million people) could lose coverage.