The Affordable Care Act will usher at least seven million more Americans into Medicaid next year, but the question of whether enough doctors will be there to welcome them is keeping some state health policymakers up at night.

A report published last year in Health Affairs signaled trouble ahead. According to that study by Sandra Decker, an economist at the National Center for Health Statistics, only two out of three primary care physicians surveyed in 2011 were willing to accept new Medicaid patients. Larger numbers said they would take on new Medicare patients or see new patients with private insurance. Medicare, health care for the elderly, is a purely federal program; Medicaid, which covers many poor people, is a joint state and federal enterprise.