Harris v. McRae, 448 U.S. 297 (1980).
The Medicaid program created by Title XIX is a cooperative endeavor in which the Federal Government provides financial assistance to participating States to aid them in furnishing health care to needy persons. Under this system of “cooperative federalism,” King v. Smith, 392 U.S. 309, 316, if a State agrees to establish a Medicaid plan that satisfies the requirements of Title XIX, which include several mandatory categories of health services, the Federal Government agrees to pay a specified percentage of “the total amount expended . . . as medical assistance under the State plan. . . . ” 42 U. S. C. § 1396b (a)(1). The cornerstone of Medicaid is financial contribution by both the Federal Government and the participating State.

Md. Dep’t of Health & Mental Hygiene v. Ctrs. For Medicare & Medicaid Srvs, 542 F.3d 424 (4th Cir. 2008). “Designed to provide medical assistance to persons whose income and resources are insufficient to meet the costs of necessary medical care, the Medicaid program functions as a partnership between the federal government and the states. 42 U.S.C. § 1396a(a)(10). After a state elects to participate in the program, the federal government shares the costs of providing medical assistance in a ratio that varies from state to state. 42 U.S.C. § 1396a(a)(2). In return, the state agrees to comply with the Medicaid statute and any administrative regulations properly promulgated by CMS. 42 U.S.C. 1396a(a)(1).”

In re Estate of Bruce, 260 S.W.3d 398 (Mo. Ct. App. 2008). “Medicaid is a cooperative federal–state program designed to assist the states in providing health care to people who cannot afford it. McNeil-Terry v. Roling, 142 S.W.3d 828, 833 (Mo. App. 2004). If a state opts to participate in the program, it must comply with all federal statutory and regulatory requirements. Id. Because Medicaid is a cooperative program, it is not susceptible to express or implied field preemption. It is susceptible only to conflict preemption.”

Wojchowski v. Daines, 498 F.3d 99 (2nd Cir. 2007). “Medicaid, which is jointly funded by the federal and state governments, is a medical assistance program authorized to pay for necessary medical care for those eligible individuals whose income and resources do not allow them to meet the costs of their medical needs.”