Medicare is phenomenally successful given its constraints. It insures more patients, for lower costs, and better care, than any comparably sized private insurer. As the standard for basic care, it can't be beat in the US. Indeed, one of the original Romneybamacare proposals was to make Medicare the baseline health insurer, covering emergencies and major health crises (like cancer), with additional or concierge treatment options to be offered by private insurers.