Since 1994 the Medicaid program in Tennessee has been known as TennCare. It operates under a special waiver from the U.S. Department of Health and Human Services (HHS) because, unlike most state Medicaid programs, TennCare benefits are paid to health care providers by insurance companies that contract with the State of Tennessee rather than by the State itself.
The Affordable Care Act (ACA) required states to expand their Medicaid programs to cover people who do not have health insurance, who are between the ages of 19 and 64, and who earn less than 138% of the federal poverty level. In 2012 the U.S. Supreme Court ruled that this provision of the ACA is unconstitutional and that Medicaid expansion should be voluntary for each state, not mandatory.
27 states have chosen to expand their Medicaid programs. Thus far, Tennessee has chosen not to do so. While it is still possible that Tennessee will change its mind, at this point that seems very unlikely.