Nick Baumann has a handy chart explaining patiently to Rick Perry et alia why Social Security is not a ponzi scheme:
As Jonathan Bernstein notes:
Very simple: anyone who says that Social Security is a Ponzi scheme either misunderstands Social Security, misunderstands Ponzi schemes, is deliberately lying, or some combination of those… After all, a Ponzi scheme is a deliberate fraud. Saying that Social Security is financed like a Ponzi scheme is factually wrong, but saying that Social Security is a Ponzi scheme or is like a Ponzi scheme is basically a false accusation of fraud against the US government and the politicians who have supported Social Security over the years.
I’m not sure, honestly, why Social Security gets so much attention. A bit of tinkering with the payroll cap, and voila! The problem is basically fixed.
The real problem facing our long-term fiscal stability is healthcare spending. For more on that you should read this ten-post series by Aaron Carroll. Unfortunately, unlike Social Security, healthcare spending will be really hard to fix, because the factors driving it are complex, and because the combination of private and public spending makes it complicated and difficult to untangle.