Posner on Means-Testing
Perhaps some politician will be bold enough to advocate that all
entitlements programs, including social security as well as Medicare,
be means-tested, as Medicaid is. There is no reason why people who can
afford to provide for their retirement should be subsidized by the
government, which is to say by the taxpayer. But such a reform does not
appear to be politically feasible.
More on means-testing here.