This is something I really didn't know.
"Under today's Medicare, seniors are subject to an individual mandate more subtle but just as coercive as ObamaCare's. By regulation, seniors must enroll in Medicare or forgo their Social Security checks. By law, they are denied the right to go outside of Medicare and buy the kind of private insurance they prefer. They are thus trapped within a single-payer government monopoly. Add budget pressures to the mix, and you have the perfect conditions for rationing."
That really does seem remarkable to me. So remarkable that I suspect it is not true, or some important fact is being left out.