Legislation recently introduced in the U.S. Senate would create a mechanism for states to offer their residents the opportunity to buy a Medicaid-based public insurance option. Eligible residents could use their premium tax credits to purchase these plans, and reduced cost-sharing requirements would apply as well. The bill could improve access to affordable health care in some states. However, there would be many differences between a Medicaid buy-in plan and existing Medicaid programs, and many of the states that could most benefit from the option would be unlikely to take advantage of it. Many of the states with low insurer participation and higher premiums in the marketplace are those that have not expanded Medicaid eligibility under the Affordable Care Act and thus are unlikely to create a buy-in option for middle-income consumers. States that have adopted the Medicaid expansion, have few marketplace insurers, and high marketplace premiums are those most likely to benefit.