@Redleg
Had Congress not raised the Social Security reserve funds for decades, they would have been earning interest to pay benefits.
In a Ponzi scheme, the capital never is invested, it is immediately paid out to early investors and the originator skims the bulk of the money.
For decades Social Security was solvent, then Congress misappropriated the capital. Congress also did not make sure the matching governmental contribution was made for each employee, thus causing the problem.
A Ponzi scheme is set up to defraud investors. Social Security was set up as mandatory retirement (and later disability) insurance. Congress defrauded the participants later on, but that was not the intent under the New Deal.