Medicaid is a health insurance program for low-income individuals and those with disabilities. Medicaid funding comes from a combination of state and federal dollars, and there are both state and federal regulations that apply to the operation of the Medicaid program. Because Medicaid is jointly run by federal and state governments, there is significant variation in Medicaid programs from one state to another (unlike Medicare, which is fully funded by the federal government, and thus very consistent throughout the country).
Elderly low-income people are eligible for both Medicare and Medicaid. (Medicaid covers long-term care, so it can be used to fund nursing home stays for people who are eligible; Medicare does not cover long-term care.)
One of the provisions of the ACA (aka Obamacare) was to expand Medicaid to cover additional low-income individuals and families, including childless adults. The federal government funds at least 90 percent of coverage for new enrollees in states that have opted to expand their Medicaid programs (federal funding covered 100 percent of the cost from 2014 to 2016; the states are gradually picking up a small portion of the cost, and will be paying 10 percent starting in 2020, with the 90/10 federal/state split remaining at that level going forward).
The Supreme Court ruled that states could decide whether or not to expand Medicaid, so not all states are expanding their programs. As of late 2017, 31 states and DC have expanded Medicaid. Maine voters approved Medicaid expansion via a ballot initiative in November 2017. If that comes to fruition, it would leave just 18 states that haven’t expanded Medicaid, although there are still questions about how Maine will fund its portion of the cost.
Medicaid is funded in part by the government and by the state where the enrollee lives. For Medicaid populations who aren’t part of the ACA’s Medicaid expansion, the federal government pays at least half of the cost of coverage, but federal funding is higher in states with lower per-capita incomes.
Medicaid eligibility for various populations differs from one state to another, particularly in states that have not expanded Medicaid under the ACA.