Medicare is not a single payer system (which is why I get confused when sibgle-payer advocates say they want “Medicsre for All”); it's more like “Obamacare with an public option for some services”; the prescription drug program (Part D) is private plans with public subsidy, and Medicare Advantage (Part C) is private plans for public subsidy as well. Parts A and B are public plans for core inpatient and outpatient services, but theres been a big push to Advantage plans (including as a vehicle to handle Medicare/Medicaid “dual eligibles”.)